"Talampakan" only applies to the underside of the foot and not of a shoe. Usually, it can have either a singular or plural meaning. The sole of a shoe, including the insole, is called "tapakán", which translates to "something stepped on".
"Talampakan" is also the very Filipino word for a foot measurement. For the "inch" though, we use the Spanish "pulgada". Sometimes you might hear it as "purgada".