If multiple phases are added to the same point in your turn, the most recently created phase happens first. For example, say you control Sphinx of the Second Sun and its ability triggers during your postcombat main phase. Later during that same main phase, another effect gives you an additional combat phase after this main phase. The additional combat will happen first, followed by the additional beginning phase.
The additional beginning phase will be a lot like your normal beginning phase. During the untap step, permanents will phase in or out as appropriate and you'll untap your tapped permanents. Anything that triggers "at the beginning of your upkeep" or similar will trigger during the upkeep step, and you'll eventually draw a card for your draw step.
After the additional beginning phase, the game proceeds to the ending phase (unless something has added even more phases; see below.)
Last observed on Scryfall 2 months ago at $2.55. Over the trailing 90 days the price moved between $2.52 and $10.52 across 45 observations. Cross-checked across TCGplayer, eBay sold, Cardmarket EU, and Star City.
This printing is one of 3 catalogued treatments from CMR — the lineup includes Foil and Nonfoil alongside the standard finish. Across our catalog the Rarix library tracks every variant in the same family so collectors can compare price, scarcity and demand inside a single lineage.
Card #99 of *Commander Legends*, the set that shipped alongside the November 2020 Commander Legends release.
Card type: Creature — Sphinx, color identity blue, printed at mythic. Mythic rares historically land in roughly one out of every eight boosters at standard print densities. Mana cost: {6}{U}{U} (8 converted). Keyword abilities: Flying.
Legal in Legacy, Vintage, and Commander.
EDHrec ranks this card #2,419 in Commander, putting it in the niche-pick tier of the format's playable pool.
Illustrated by Antonio José Manzanedo. Rarix catalogs 308 other cards credited to this artist.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Antonio José Manzanedo
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
Even if you don't attack with any creatures during combat, you'll still get a postcombat main phase and Sphinx of the Second Sun's ability will still trigger.
The additional beginning phase all happens during the current turn. Any effects that last "until your next turn" or similar won't expire just because you'll go through an additional beginning phase.
If you somehow have more than two main phases in a turn, each main phase other than the first one is a postcombat main phase, and Sphinx of the Second Sun's ability triggers at the beginning of each of them.
