I have one theory. Looking at the example website posted on the Superform stack number entry area discussion:-
The telephone number input has been configured as a ‘text’ input type, within the source code. If a browser is trying to be smart and do some self-validation, it may unintentionally be blocking use of the number keypad when you enter content in this field. The browser might be thinking “why is this person trying to enter numbers in a text box?”
Changing the telephone input (probably through means of a stack update) to use either a number or dedicated tel input type instead might give better results.
So:
<input id="input-stacks_in_111282_page15" name="input-stacks_in_111282_page15" class="floatLabel hasError" type="text" value="" required="required">
Becomes:
<input id="input-stacks_in_111282_page15" name="input-stacks_in_111282_page15" class="floatLabel hasError" type="number" value="" required="required">
Or even better:
<input id="input-stacks_in_111282_page15" name="input-stacks_in_111282_page15" class="floatLabel hasError" type="tel" value="" required="required">
Might be worth a shot. This change might also help with auto-complete on the form inputs too.