This is a numeric field type, however, since it stores phone numbers, there are some symbols that are allowed for formatting purposes such as parenthesis () and hyphens -
Configuring a Phone Field
Give your field a name and add a field hint if desired. You can then select the section in which the field will be created or keep the default option.
The field type must be set to 'Phone'.
If desired, you can set a default value for all new records. Team members will have the option to override the default value if needed.
Phone fields can also be calculated. Just enable the 'Calculated' checkbox and add your custom code in the space available for it.
Enable the 'Required' checkbox if the information for this field is mandatory. It means that if you enable this option, every time a team member creates a new record, they will need to input a phone number in this field in order to save it.
Phone fields can be set up as 'unique'. This means that the system will prevent duplicates of the Phone values from being added to the system. It is recommended to set up the Phone as a Unique field if there shouldn't be any duplicates. It helps prevent that team members add the same phone for different records.
If you enable the 'Lock After Create' as its name implies, the field will be locked once the new record is saved and the value of the field will not be editable afterward.
Once you are done setting your field, click the save button.
Note: All new fields are added at the bottom of the form.