Nigeria is very much unclear on the concept of the president handing over. The Acting President is the de-facto president right now.
PMB can not be taking calls from presidents all over the world, while he is not in the saddle. That is not constitutional.
Despite the fact that some Nigerians have been making noise wrongly that that the president should address the nation, PMB is actually not responsible to Nigeria right now.
If he is well enough for his job, he should please write back to the Senate to take over again, and the acting president can revert to his VP job.
He can actually continue to sit in England for the rest of his treatment and delegate the VP to do the heavy lifting in Nigeria. Right now, it would appear that he has cleverly converted a medical leave to a working vacation, illegally.
He should resubmit papers to the NA to take his job back, then we will know that he is properly on a working vacation. The confusion at the moment is not good for the nation. You cannot hand over and still continue to cherry pick any part of the job that tickles your fancy. In doing so, he is (inadvertently) undermining the acting president.