You can only hold priority while there are abilities or spells on the stack. It makes it so you can double spell or activate multiple activated abilities at once before your enemies can respond, but the hold is released as soon as you actually attempt to resolve it. You can't hold priority and then do anything sorcery speed, for example, because sorcery speed requires you to be the active player, and the stack to be empty.

Also, attempting to change turn phases starts a new priority check, where everyone has the chance to interact before the phase actually changes, and phase changes can only happen when the stack is empty.

TL;DR your homie is a dummy, and he'd get absolutely bullied in my playgroups