How to cover up old phone outlet where there is tile already in place?

You can buy a plate that is solid and paint it to match the tile, then place something decorative in front of it.

The simplest solution may be to just glue the old cover back in place and paint same color as tile.

If you have any tile pieces around you may be able to use them to camouflage your hole (after gluing a base in).

In my old house, I hung a picture on my backsplash where I had removed an ancient wall exhaust fan. It worked for years until we permanently fixed it! Lol!

looks like a place for at least one screw.Just from what I can see from the picture,I would pack full of insulation,carefully stuffing all cracks;etc,then try putting a blank cover plate over using the one screw and construction cement,hot glue,or some other really good adhesive.Gorilla glue has one that has to be used by wetting the surfaces,that I use to put auto window glass (door) into the tracks.It is the only glue I've found that holds in this situation,so it might work for the cover plate.

Air pouring in? insulate! Then find a piece of tile from a tile company. Call around and see if they have a discard pile they will let you go through. If you are lucky to find the right size [or they will cut for you] use silicone adhesive to cover the hole.

You can buy blank plates that cover these blue wire boxes. Note that there is a screw hole at the bottom, and probably one at the top under the other plate. You can, as others have said, use the bottom hole, and glue the other, top hole part of the plate, in place with silicone caulk.

since you are leaving the existing phone wiring, you should just put a blank faceplate over that spot. You can decorate that faceplate many different ways if you wanted something with a little design.

It's always best to not cover wiring with anything permanent since you never know if you'll need to get to them, or if you sell your home, if the new homeowner would want those phone wires.

If you do not intend to use the phone jack ever, get the foam spray to insulate the area. It will fill up the hole. Then get a tile cut at Lowes or Home depot and glue it in place. You can paint the tile to match or get one that contrasts.

Get something called Great Stuff. It's spray in insulation and expands a lot! It will fill in the hole and then harden like foam. You can trim it to size and then have something to either glue a blank plate to or piece of tile. 😎

Maybe a little piece of wood or drywall and some texture on top and paint? It is really small. It should not be too difficult

You can use drywall or wood and then use some paint to cover it up