diff --git a/app/constants.py b/app/constants.py
index fb547ce263..bc297bf7bd 100644
--- a/app/constants.py
+++ b/app/constants.py
@@ -330,16 +330,3 @@ class CacheKeys:
 
 # Admin API error codes
 QR_CODE_TOO_LONG = "qr-code-too-long"
-
-
-# We updated the content for phone number validation messages in https://github.com/alphagov/notifications-utils/pull/1054,
-# but these are returned from our API. We don't want to make any breaking changes, so we will map them back to our
-# original errors.
-# We can decide as/when we want to remove this and update the messages to end users.
-PHONE_NUMBER_VALIDATION_ERROR_MAP = {
-    "Mobile numbers can only include: 0 1 2 3 4 5 6 7 8 9 ( ) + -": "Must not contain letters or symbols",
-    "Mobile number is too long": "Too many digits",
-    "Mobile number is too short": "Not enough digits",
-    "Country code not found - double check the mobile number you entered": "Not a valid country prefix",
-    "This does not look like a UK mobile number – double check the mobile number you entered": "Not a UK mobile number",
-}
diff --git a/app/notifications/validators.py b/app/notifications/validators.py
index d424ebb7b3..857c8ea8f9 100644
--- a/app/notifications/validators.py
+++ b/app/notifications/validators.py
@@ -21,7 +21,6 @@
     KEY_TYPE_TEAM,
     KEY_TYPE_TEST,
     LETTER_TYPE,
-    PHONE_NUMBER_VALIDATION_ERROR_MAP,
     SMS_TYPE,
 )
 from app.dao.service_email_reply_to_dao import dao_get_reply_to_by_id
@@ -277,7 +276,3 @@ def check_template_can_contain_documents(template_type, personalisation):
         isinstance(v, dict) and "file" in v for v in (personalisation or {}).values()
     ):
         raise BadRequestError(message="Can only send a file by email")
-
-
-def remap_phone_number_validation_messages(error_message):
-    return PHONE_NUMBER_VALIDATION_ERROR_MAP.get(error_message, error_message)
diff --git a/app/schemas.py b/app/schemas.py
index 8c7a556266..2e8a66a786 100644
--- a/app/schemas.py
+++ b/app/schemas.py
@@ -25,7 +25,6 @@
 from app import db, ma, models
 from app.dao.permissions_dao import permission_dao
 from app.models import ServicePermission
-from app.notifications.validators import remap_phone_number_validation_messages
 from app.utils import DATETIME_FORMAT_NO_TIMEZONE, get_template_instance
 
 
@@ -134,8 +133,7 @@ def validate_mobile_number(self, value):
             if value is not None:
                 validate_phone_number(value, international=True)
         except InvalidPhoneError as error:
-            error_message = remap_phone_number_validation_messages(str(error))
-            raise ValidationError(f"Invalid phone number: {error_message}") from error
+            raise ValidationError(f"Invalid phone number: {error.get_legacy_v2_api_error_message()}") from error
 
 
 class UserUpdateAttributeSchema(BaseSchema):
@@ -175,8 +173,7 @@ def validate_mobile_number(self, value):
             if value is not None:
                 validate_phone_number(value, international=True)
         except InvalidPhoneError as error:
-            error_message = remap_phone_number_validation_messages(str(error))
-            raise ValidationError(f"Invalid phone number: {error_message}") from error
+            raise ValidationError(f"Invalid phone number: {error.get_legacy_v2_api_error_message()}") from error
 
     @validates_schema(pass_original=True)
     def check_unknown_fields(self, data, original_data, **kwargs):
@@ -578,8 +575,7 @@ def validate_to(self, value):
         try:
             validate_phone_number(value, international=True)
         except InvalidPhoneError as error:
-            error_message = remap_phone_number_validation_messages(str(error))
-            raise ValidationError(f"Invalid phone number: {error_message}") from error
+            raise ValidationError(f"Invalid phone number: {error.get_legacy_v2_api_error_message()}") from error
 
     @post_load
     def format_phone_number(self, item, **kwargs):