Phases

Let's go through the structure of a turn in magic - read more here turn structure:

1. Untap step
   • phased out cards phases in, card on the battlefield with phasing phases out. Tapped permanents that phases in, gets to untap.
   • The player whos turn it is, untap all permanents that are able to untap.
2. Upkeep step: pay upkeep and play abilities that can only be played in the upkeep. Upkeep itself is a triggerede ability, hence it is placed on the stack.
3. Draw step:
   • You draw a card.
   • Abilities that trigger at the beginning of the draw step, goes on the stack
   • You gain priority.
4. Main phase 1: here you can cast things at sorcery speed plus lands.
5. Combat phase: attack
6. Main phase 2: same as main phase 1.
7. End step: last chance to peform actions before next players turn.

Mana in your mana pool is emptied between each phase. That's also true for your mana during your opponent(s) phases.