Why a Tomcat's missile load depends on its hardpoints

Could an upgraded F-14 carry ten or more AMRAAMs because it could carry six Phoenix missiles?

Possibly, but the hardpoints would probably need modification, and both missile weight and mounting arrangements would matter.

An imagined upgraded F-14 would serve as a long-range carrier of AMRAAM missiles. Its ability to carry six Phoenix missiles does not by itself establish that it could carry ten or more AMRAAMs. Missile weight and the available hardpoints both constrain the load. Reaching the suggested number would probably require modifications to the weapon stations.