I can't re download it or find it in the windows phone store.
I'm sure that's where the confusion started, Spartan assault (where both links go to) is the game for WP8; Spartan ops is a gamemode in Halo 4.Are you sure you mean the right app cause I can't find any app for WP that's called "Spartan Ops", only "Halo Spartan Assault" and "Halo Waypoint" (both still available in the Store)?
"Spartan Ops" on the other hand is an add-on for Halo 4 on the X360.