I have played Single player and afk after a few nights and phantoms spawned, but after playing on 1.14 server and doing the same, no phantoms has spawned at all, even after not sleeping for days while being alone on the server, no phantoms spawn at all. seems like a server bug on it's own.
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There where no block nor any sign or noise of any phantoms above my head, just the normal mobs... note that this is only on the 1.14 server, the normal single player has phantoms. and yes I was on the surface.. pillared up to avoid ground mobs, but still no phantoms... a bit worried if I can repair elytra if no phantoms on the server without mending books.
You're probably experiencing MC-147890 then.

This issue can't be a duplicate and I don't see a fix on the other reported issues... This issue is that only phantom mobs are not spawning on the Server of 1.14. Yet they will spawn in a Single player world. Every other mob as well as the aggressive mobs do spawn on the Server.
This is the .JAR server file downloadable from the Mojang Website and there is no setting I can find to change this.
Were you on the surface on the 1.14 server? (Meaning, no blocks above your head)