In Phleum pratense, each side of the spikelet extends up in a short, stout awn, giving the spikelet more the shape of the "hook-em-horns" gesture of the University of Texas at Austin, and the glumes are not winged but have a few coarse hairs. The spikelets often spread out at 90 degrees from the axis, and the other ones often point downward a bit. There is often more of a white-spotted look in Phleum inflorescences than in Alopecurus, which may be useful (or confusing) with out-of-focus photos. Phleum doesn't seem to bloom before June in North America, and generally not in early June. Be very suspicious of spring reports of Phleum pratense.

In Alopecurus pratensis, the sides of the spikelets slope inwards, giving each spikelet a pointed tip, near the center. Also, this plant has hair-like awns, a trait of Alopecurus pratensis, not of Timothy. Alopecurus blooms much earlier in the year than Phleum pratense. The spikelets are generally oriented upwards.

Alopecurus arundinaceus resembles A. pratensis, but has short, hair-like awns. If it's mature enough, the glume tips spread a bit. It's present in North America and nearly always overlooked.

Phalaris: The sides of the spikelets slope inwards, giving each spikelet a pointed tip, near the center. In many species, glumes are winged. In Phalaris arundinacea, the inflorescence tends to be lobed, and often a distinct short branch is visible near the bottom. Habitat is wetlands (at least seasonally wet spots). Phalaris arundinacea is rhizomatous; Phleum is cespitose. Confusion of Phalaris species with Phleum is especially common in California.

I hope that anyone willing to work on Phleum pratense identifications is aware of what Plantago lanceolata and other plantago species look like, but clearly a lot of people on iNaturalist are not.

Sometimes, if there isn't a good close photo of the inflorescence, you really can't tell if you're looking at Phleum, Alopecurus, or Phalaris.