Double vision only when looking down at phone, what to do?

Opthalmologist: If this is something that is new, it would be a good idea to have this evaluated by a opthalmologist or better yet a neuro-opthalmologist. The eyes move in a complex manner that is controlled by the brainstem. You may have have some involvement of certain cranial nerves. Specialized testing can help determine the which nerves and thus target the further investigations (ie. MRIs).