Put the second phone on silent so that it won't give away its location if the OW contacts your H.
Do you have a charger that would fit it?
Keep that phone somewhere really, really safe.
Do you have a fairly full container of new cat litter? Put the phone in a little tupperware container and bury it deep in the new litter.
Or deep in a big bag of kibble if you have a dog.
Or hamster hay/pellets, etc.
Same idea - big jar of couscous or rice.
Can you remove the grille on the bottom of your fridge? If yes, you might be able to stick the phone in a little shallow tupperware container and stow it under the fridge. Replace the grille. If it's filthy, resist the temptation to clean it. Check for the overflow valve and for drips first.
Or put it into a sock, knot it, cut any extra bit of sock at the top so it's not a big, bulky thing, and attach it to the top of some thick curtains, around the back, preferably in the folds and in an area that doesn't pull across the window so it won't be disturbed daily and the light shining through the curtains won't expose a peculiarly shaped shadow. You can use big safety pins to attach it jut below the rod. Lined curtains work best for this, and you can also secrete it between the lining and the curtain (best with stiff fabric though). Be careful that the screen of the phone points to the wall or it might light up and give the game away if she contacts your H with it. Check how this works before you decide this is The Place.
Do you have a large table lamp that has a felt bottom? Maybe you could take off the bottom and shove the phone into the cavity?
Do you have an almost full box of tissues? Open the box carefully (at the bottom or sides, depending on where it is sealed) and take out enough tissues to make room for the phone, leaving the tissues on top undisturbed. Roll the tissues you take out to fill in the cavity at either side of the phone to keep the top tissues from falling down at the sides and to prevent rattling if H shakes the tissue box. Close the box up again, and keep it beside your bed or in your bedside table if you have one.
Do you have a bicycle? Hide it under the saddle. Disguise it with something that matches the colour of the underneath of the saddle (a black sock for instance).
Or cut a little slit in your mattress at the back near the seam on your side of the bed and slip the phone in. Works best if you cut the slit at the bottom of the mattress and if you put it into a small tupperware container first.
Delete your history on all devices you use.
Change your passwords on MN and all email addresses you use.