r after any vowel has a special place in english.
oor usually end up as ʊɚ, ɔɚ, oʊɚ
poor: pʊɚ
moore: mʊɚ, mɔɚ, moʊɚ
floor: flɔɚ, floʊɚ
door: dɔɚ doʊɚ
oo before any but r:
boom: bum
doom: dum
hood: hʊd
good: gʊd
wood: wʊd
hook: hʊk
food: fud
proof: pruf
school: skuo (the last o shud be transcribed as a satellite, since vocalized l shud be there).
Now, you can notice the pattern.