Phone Field Error Checking

I use clickfunnels, and ontraport code for the optin form. I use phone to capture and text people. I switched from INfusionsoft recently and had no issues capturing a customers data in this manner. Ontraport does not error check phone or sms field. The field is not required and since it doesn't error check, it submits the page and hangs without capturing data or asking the person to correct it. Would be nice if it did so I can use the SMS field and text people that are giving me their information. Any way to have a webform using html code get redirected to hosted version on Ontraport where the prospect will be notified that the phone field wasn't filled out correctly?