In case you haven't realized, but every phantom emits a throbbing noise, you just have to listen carefully. This has been somewhat helpful to me when I'm invaded, I'll know when to use caution when I hear the noise.
This also applies to friendly phantoms as well, you will hear the noise about 2 seconds before the phantom has spawned, so you will know that your summon was successful before he/she actually appears in your world.
This also applies to friendly phantoms as well, you will hear the noise about 2 seconds before the phantom has spawned, so you will know that your summon was successful before he/she actually appears in your world.