Can We Cast Out a Demon That Is Not Physically Present with Us?

Yes, though this is not the usual way to do it.  The pattern is to minister personally to the demonized person.  However, the following two cases in Scripture show that there can be exceptions to the rule.

In Matthew 15:22-28 and Mark 7:25-30, the demon was nowhere near Jesus and the demonized daughter’s mother, but it still had to leave when Jesus spoke.

In Acts 19:11-12, no explicit command was used, but an anointed cloth brought to demonized people made the demons leave.  We used this method in a Healing School class where we anointed an item to be taken to someone’s mother who was in an insane asylum.  The demon left and the mother was promptly discharged.