Yes and no. It depends on what place you're talking about.
With Krabi, I found that even the so-called 'hostels' were usually more standard 'hotel-like' in feel, or at best the atmosphere was like that of boutique hotels. You can still find dorms (if that's what you're looking for) in Krabi as well as 'hostel-like' prices for hotels, but I didn't find a place which gave the typical hostel experience. Maybe I didn't look around much. To be honest, I was just glad every now and then to have the comfort of a hotel at hostel prices.
Phuket is a different beast. Public transport is almost non-existent on the island and the actual action is all in the beaches on the island, not Phuket Town. Having said that, it's very possible to get hostel accommodation in Phuket Town and then head out to one of the beaches after a lazy lunch, then stagger back home next morning after some crazy partying. Phuket Town has a quite a few good hostels; I particularly recommend Phuket Backpacker Hostel - the staff, the vibe, the crowd - everything is excellent! (They've two incredibly friendly dogs, a huge DVD collection, and a pool table / bar downstairs. Oh and there's a really nice classy-looking-but-cheap restaurant a few doors away from them.) There are others too, from other backpackers I met. Shop around.
There are cheap hotels / guesthouses near the major beaches in Phuket such as Patong, Bang Tao et al too - just like with Krabi. I didn't stay in them though. Similar vibe: hotel-ly, cheap enough.