Should be phone number, not form number.  Sorry!

What is it doing now?  The behavior you are describing is the default when you start typing.

If I tab to the field, the cursor is placed on the far left of the field, which is what I want.  If I click on the field, the cursor can be placed anywhere in the middle of the field.  How do I force it to start at the far left if the field is blank?

The screenshot below shows one way to accomplish this.
I sent the Field Name to the Sub Routine so it can be used with other fields on my form.