Aphetto Alchemist does not have summoning sickness.
({W} magic symbol) available.
Steps
Activate Aphetto Alchemist by tapping it, targeting Halo Fountain.
Holding priority, activate Halo Fountain's first ability by paying ({W} magic symbol) , tapping it and untapping Aphetto Alchemist, creating a 1/1 Citizen creature token.
Resolve the Aphetto Alchemist ability, untapping Halo Fountain.
Activate Phyrexian Altar by sacrificing the Citizen token, adding ({W} magic symbol) .