-snip for character limit -
Here, he's amped two-fold - once by a wand that improves existing spells (which, using common sense, would suggest that transportation via portals could be upgraded to teleportation) and once by an item that enhances any powers its wielder possesses (again, on top of the wand especially, this should upgrade portal generation to teleportation).
All of this makes even more sense when you consider that, in an amped environment, Strange has already demonstrated the ability to teleport.
Nothing shown in the Sanctum suggests Strange is amped as much as someone wielding
either the Elder Wand or One Ring, let alone
both of them.
Moreover, basic wands in Harry Potter allow their wielders to "apparate",
which IS teleportation. The Elder Wand is far more powerful than any other wand in the Potterverse. And, in turn, IT is amped by the One Ring.
Strange now has the Elder Wand, the One Ring, a Sling Ring enhanced by both of those items, and experience of teleporting. Literally anything shown on screen before is massively amped.
Any other questions re: that?