[Engineering] Trial form: Verify phone number field content

Problem

Defined in epic

Potential solution

Telephone numbers are widely different across countries so we can not apply a specific pattern for numbers here. That being said, we can explore the following solution:

• Verify that the telephone number field does not contain letters.
• Run a check to see if the phone number is valid.

The validation pattern could be the following

<input type="tel" pattern="\+[0-9- ]*" required>