You can use the formula below in the Calculated Fields to automatically include the country dial code (e.g. +44) to the shipping address' phone number field based on the shipping address' country:

"+" + strip_non_numeric_chars({{ shipping_address.phone }}).lstrip("0") if {{ shipping_address.phone }}.startswith("00") else get_attribute_value('{"AF": "+93", "AX": "+358", "AL": "+355", "DZ": "+213", "AS": "+1684", "AD": "+376", "AO": "+244", "AI": "+1264", "AQ": "+672", "AG": "+1268", "AR": "+54", "AM": "+374", "AW": "+297", "AU": "+61", "AT": "+43", "AZ": "+994", "BS": "+1242", "BH": "+973", "BD": "+880", "BB": "+1246", "BY": "+375", "BE": "+32", "BZ": "+501", "BJ": "+229", "BM": "+1441", "BT": "+975", "BO": "+591", "BA": "+387", "BW": "+267", "BR": "+55", "IO": "+246", "BN": "+673", "BG": "+359", "BF": "+226", "BI": "+257", "KH": "+855", "CM": "+237", "CA": "+1", "CV": "+238", "KY": "+ 345", "CF": "+236", "TD": "+235", "CL": "+56", "CN": "+86", "CX": "+61", "CC": "+61", "CO": "+57", "KM": "+269", "CG": "+242", "CD": "+243", "CK": "+682", "CR": "+506", "CI": "+225", "HR": "+385", "CU": "+53", "CY": "+357", "CZ": "+420", "DK": "+45", "DJ": "+253", "DM": "+1767", "DO": "+1849", "EC": "+593", "EG": "+20", "SV": "+503", "GQ": "+240", "ER": "+291", "EE": "+372", "ET": "+251", "FK": "+500", "FO": "+298", "FJ": "+679", "FI": "+358", "FR": "+33", "GF": "+594", "PF": "+689", "GA": "+241", "GM": "+220", "GE": "+995", "DE": "+49", "GH": "+233", "GI": "+350", "GR": "+30", "GL": "+299", "GD": "+1473", "GP": "+590", "GU": "+1671", "GT": "+502", "GG": "+44", "GN": "+224", "GW": "+245", "GY": "+595", "HT": "+509", "VA": "+379", "HN": "+504", "HK": "+852", "HU": "+36", "IS": "+354", "IN": "+91", "ID": "+62", "IR": "+98", "IQ": "+964", "IE": "+353", "IM": "+44", "IL": "+972", "IT": "+39", "JM": "+1876", "JP": "+81", "JE": "+44", "JO": "+962", "KZ": "+77", "KE": "+254", "KI": "+686", "KP": "+850", "KR": "+82", "KW": "+965", "KG": "+996", "LA": "+856", "LV": "+371", "LB": "+961", "LS": "+266", "LR": "+231", "LY": "+218", "LI": "+423", "LT": "+370", "LU": "+352", "MO": "+853", "MK": "+389", "MG": "+261", "MW": "+265", "MY": "+60", "MV": "+960", "ML": "+223", "MT": "+356", "MH": "+692", "MQ": "+596", "MR": "+222", "MU": "+230", "YT": "+262", "MX": "+52", "FM": "+691", "MD": "+373", "MC": "+377", "MN": "+976", "ME": "+382", "MS": "+1664", "MA": "+212", "MZ": "+258", "MM": "+95", "NA": "+264", "NR": "+674", "NP": "+977", "NL": "+31", "AN": "+599", "NC": "+687", "NZ": "+64", "NI": "+505", "NE": "+227", "NG": "+234", "NU": "+683", "NF": "+672", "MP": "+1670", "NO": "+47", "OM": "+968", "PK": "+92", "PW": "+680", "PS": "+970", "PA": "+507", "PG": "+675", "PY": "+595", "PE": "+51", "PH": "+63", "PN": "+872", "PL": "+48", "PT": "+351", "PR": "+1939", "QA": "+974", "RO": "+40", "RU": "+7", "RW": "+250", "RE": "+262", "BL": "+590", "SH": "+290", "KN": "+1869", "LC": "+1758", "MF": "+590", "PM": "+508", "VC": "+1784", "WS": "+685", "SM": "+378", "ST": "+239", "SA": "+966", "SN": "+221", "RS": "+381", "SC": "+248", "SL": "+232", "SG": "+65", "SK": "+421", "SI": "+386", "SB": "+677", "SO": "+252", "ZA": "+27", "SS": "+211", "GS": "+500", "ES": "+34", "LK": "+94", "SD": "+249", "SR": "+597", "SJ": "+47", "SZ": "+268", "SE": "+46", "CH": "+41", "SY": "+963", "TW": "+886", "TJ": "+992", "TZ": "+255", "TH": "+66", "TL": "+670", "TG": "+228", "TK": "+690", "TO": "+676", "TT": "+1868", "TN": "+216", "TR": "+90", "TM": "+993", "TC": "+1649", "TV": "+688", "UG": "+256", "UA": "+380", "AE": "+971", "GB": "+44", "US": "+1", "UY": "+598", "UZ": "+998", "VU": "+678", "VE": "+58", "VN": "+84", "VG": "+1284", "VI": "+1340", "WF": "+681", "YE": "+967", "ZM": "+260", "ZW": "+263"}', {{ shipping_address.country_code }}) + strip_non_numeric_chars({{ shipping_address.phone }}).lstrip("0") if ({{ shipping_address.phone }} and "+" not in {{ shipping_address.phone }}) else strip_non_numeric_chars({{ shipping_address.phone }}, except_chars="+")

The formula will perform the following:

• Only add the country code if the "+" sign doesn't already exist in the phone number (since the customer might already include the country code if the customer's phone number is from a country that's different from the shipping address' country).
• If there are two 0s in front (e.g. 0044123456789), simply replace "00" with "+" as this will typically be followed with the country code.
• If there's a leading 0 in the phone number, strip that out before adding the country code.
• Strip out non-numeric characters (except the "+" character) from the phone number.

Examples:

1. If the value of the shipping_address.phone field is 078 155 5555 and the shipping address country code is "GB", then the formula will output +44781555555.

2. f the value of the shipping_address.phone field is +1 (781) 555-5555, then the formula will output +17815555555.

Replace "shipping_address" with "billing_address" in the formula to apply the same for the billing address phone.