clean-up
514.2. Second, the following actions happen simultaneously: all damage marked on permanents (including phased-out permanents) is removed and all “until end of turn” and “this turn” effects end. This turn-based action doesn’t use the stack.
514.3. Normally, no player receives priority during the cleanup step, so no spells can be cast and no abilities can be activated.

Untap
502.3. No player receives priority during the untap step, so no spells can be cast or resolve and no abilities can be activated or resolve. Any ability that triggers during this step will be held until the next time a player would receive priority, which is usually during the upkeep step. (See rule 503, “Upkeep Step.”)

Upkeep
503.1. First, any abilities that trigger at the beginning of the upkeep step and any abilities that triggered during the turn’s untap step go on the stack. (See rule 603, “Handling Triggered Abilities.”)
503.2. Second, the active player gets priority. Players may cast spells and activate abilities.