personal hotspot is greyed out on my iphone

greyed out usually means cellular data itself is off or the carrier hasn't provisioned tethering on your line. check Settings > Cellular > Cellular Data is on first. then Settings > General > About and wait a few seconds, if a carrier settings update pops up install it. if still grey do Reset Network Settings under Transfer or Reset iPhone, you'll need to rejoin wifi after. if that doesn't bring it back it's a call to the carrier, they can re-push the hotspot feature to the SIM even when the plan says it's included.