Did Minecraft 1.13 change the way iron golems spawn?

Yes, 1.13 did have several bugs related to iron farms.

• Villager detection was changed from 15 to 16 blocks
• Door detection order was changed
• Iron golems spawn in the air

The first two are claimed to be fixed by the snapshot 18w30a, but do not use that snapshot since it has a very common game crashing bug. 18w30b seems to be stable however.

Another change that will affect the Iron Phoenix is that villagers swim up water faster, which changed the timing of the water climb from around a minute to 15 seconds. This can be fixed by implementing something to hold the villager from the water column for a while, like this. The rest of the video seems like it can be ignored because of the bug fixes from 18w30a.

I am currently seeing if these fixes work by having my iron farm rebuild itself, but so far it doesn't look too promising because golems are spawning in the air under the eastern and western door pads.

As of 18w31a, the Iron Phoenix works as long as you implement the water column change.