By default, CheckView uses a U.S. phone number format for test flows. However, for those who require international phone number formats (e.g., +44 for the UK), options are available based on your plan to accommodate various formats that are enforced by your form logic.
For example in Gravity Forms, you can set either US or International Format:

Default U.S. Format
CheckView’s standard phone number format follows U.S. conventions (e.g., (123) 456-7890). This is automatically applied in test flows unless adjusted for an international format.
For Higher-End Plans: Changing Phone Number Format in Organization Settings
On CheckView Advanced plans, you can modify the default phone number format for all tests within your organization to support international formats. This can be done in the Variables section of your organization settings.
For Lower-End Plans: Adjusting Phone Number Format on a Per Test Flow Basis
For plans without organization variables, international phone numbers must be set up individually within each test flow.
For phone fields that use the international telephone input (the field with a country flag dropdown), CheckView enters the number with a dial code prefix so the field accepts it, instead of opening the country dropdown. This is applied when a test flow is generated, so newly generated or rebuilt flows use it automatically. Existing flows are unchanged until you rebuild them. The default dial code is +1, so to test a specific country format you can still set the value using the Variables method described above.