As mentioned, the pickpockets go after that which is easily accessible, so it's essential that anything important to you is not.
A wrist lanyard that attaches to the phone is excellent for hanging onto your phone while out and about before storing it safely each and every time. My phone is always attached to my wrist with the lanyard when not in a secure pouch or bag.
For your husband, consider something like this
It's best to choose one that's just large enough for passport (while in transit), phone, cards, cash. Should hold the phone snugly, but not be too roomy.
With the belt loop attachment, it's worn between the shorts and himself. It can be worn outside most of the time, if you don't mind it flopping with every step, but it's best to secure it well ahead of going into a metro/RER station.
For sure, check the airport shops. Securing your phone is not the time to quibble too much over cost. But, do choose carefully.
No, not a front pocket. A seasoned traveler on the TA forum reported recently that his phone was lifted as he got onto an RER train with the thief running off the train and the doors closing right behind him. For sure, the thief took notice of where he put it as he was getting on the train. And, I've seen many a phone slide out of a front pocket and onto the sidewalk at a nearby table, unnoticed by the owner.
For yourself, you may want to re-think a cross body bag, which does not have to be large or heavy - just large enough for the phone and other small essentials. A wrist wallet becomes a huge nuisance very quickly. Hands free is better.
This has been the perfect bag for me
I use the inside zipper pocket for the phone. The outside zipper pocket is really handy if you'll have a Navigo (locate the chip and you'll know which area to wave over the scanner without removing the pass) or other transit passes/tickets. All weighs just under a pound. I nearly never remove the bag, even when using rest rooms. The trick to cross body bags is weight and comfortable strap. If necessary, you can hold the bag in your hand as you're walking. Or, have your husband carry both phones in the bag when not in use, or for a break. Or, you can adjust the shoulder strap and wear it around your waist.
A good place to find a large selection of small cross body bags is BHV, Galeries Lafayette, etc. But, first check the roving markets where you'll often find not only great selection but, often, the exact same products for considerably less.
Otherwise, you may be happy with the belt loop model if you can find one that fits your phone.
If you'll be using your phones for battery draining apps such as the camera, Google Maps, you may want to seriously consider a portable battery charger. (I carry mine in the bag with the phone. We share one 16750mAh which is more than enough for our Androids with heavy use.)