Form - Lead Field - Core Number

I have a number of forms to generate lead details, including their contact number using the core number option. Potential leads are inserting an email ID here instead of a contact number and are able to submit the form. Is there an option that prevents this and only allows numbers and the + sign please?

I have a number of forms to generate lead details, including their contact number using the core number option. Potential leads are inserting an email ID here instead of a contact number and are able to submit the form. Is there an option that prevents this and only allows numbers and the + sign please?