Explanation of phasing

I'm having a lot of problems with this phasing. Mount Hyjal was almost empty for me - I had to grind RDF's to level up, Deepholm has like 5 working quests and Twilight Highlands is completely empty as well except dragonmaw port. What do I need to do? Finishing the quest is impossible since this is an elite with 322k hp.

Can I just get "unphased" somehow? I literally only need quests in the area and mobs for professions.

I`m not sure if it`s about phasing.

To get the questline in Mount Hyal, Uldum starting you need to visit the board in either stormwind or orgrimmar and get the starter quest.
The quests you need begin with "Hero`s Call".

After that you`ll find loads of quests in those areas.