Fix phone number input field validation

[akshay0611]

This PR fixes the phone number input field to ensure that it only accepts numbers, along with the symbols + and -. The following updates were made:

• Applied pattern validation to restrict input to numbers and symbols + and -.
• Set the inputmode="numeric" to show the numeric keypad on mobile devices.
• Added an onkeypress event to restrict non-numeric characters from being typed into the field.

These changes will improve form validation and prevent incorrect phone numbers from being entered.

It closes Issue #22