The X-Men are attacked by the Phalanx, mutant-hating humans who have used the alien Warlock's techno-organic virus to turn into techno-organic beings themselves. With these powers, the Phalanx are able to change their shape and assimilate organic matter. As the Phalanx they are a hive mind, programmed to destroy all mutants.
The main parts of the story take place in the following issues:
Uncanny X-Men 316
X-Men 36
Uncanny X-Men 317
X-Men 37
X-Factor 106
X-Force 38
Excalibur 82
Wolverine 85
Cable 16
I have also included Uncanny X-Men 305-306 and 312-313 as they contain the first fights between the Phalanx agents and the X-Men.
In addition I have included Excalibur 78-80 which lead into Phalanx Covenant story and introduces of Douglock, who is an amalgamation of the New Cypher and Warlock.
Enjoy and please seed