Black holes are a gravitational phenomenon.
However, an object with electric charge (and black holes can have electric charge) creates an electromagnetic field around it. The energy and momentum in this field are included in the energy-stress tensor, the source of gravity in general relativity. So the spacetime *metric* (which describes how spacetime is curved) is a bit different for a charged body than for an uncharged body.
But again, although the electric charge of the body does ultimately affect spacetime, it's not really the charge *per se* that matters, but rather the energy and momentum in the electromagnetic field. And, of course, it's all just a source term included in equations that describe *gravity*, not electromagnetism. So there is really no such thing as "a black hole from electromagnetism".