Do you think it is a good idea to use telephone component in adaptive forms to use as a numeric field because it's input type is tel, so that the number keypad pops up for phones. Where as for the numeric field component, the input type is text.
If the only functionality that you are trying to get by using a telephone field is the number pad pop up on mobile, have you tried setting the following field under basic settings for the "Numeric Box" component?
If the "Numeric Box" still doesn't work as required, you could also create a custom widget based on the numeric box and extended it.
If you still want to use the telephone field for other reasons, then you should make sure it works as you expect by testing thoroughly. If you are using AEM 6.3, you could write test cases using calvin to:
* check alpha characters are rejected,
* the comparison functionality in your other post works
* ensure numbers are handled etc.
It will also help if you decide to swap the component for a different one later as well as the tests will prove that it works.