These problems can be quite difficult to solve. If the RF source is close to your equipment and you can't increase the distance (or can't increase it sufficiently), it may prove impossible to solve the problem, though you may be able to reduce the effect of the interference.
It all depends on where the interference is being "detected" (converted into audible signal energy); there may be more than one such point in the circuit. Increasing the distance between the source of the interference and your equipment is the first thing to strive for. As a close second, keep the connections among all your items of equipment as clean, short and direct as possible. Try reorienting cables and other pieces because the angle of signal incidence may affect the strength of the received signal. It is basically like trying to improve reception of a distant radio station that you want to listen to, except exactly in reverse; you want to arrange the worst possible receiving setup for the signals you're receiving in this case.
As mentioned, Neutrik EMC connectors on your XLR-3 cables can definitely help; Schoeps' XLR-3 microphone cables use these; I'm amazed that everyone else's do not (and I'm a bit dismayed that Schoeps' XLR-5 to XLR-3 "Y" cables don't use them). Sescom, by the way, sells XLR-3M to XLR-3F barrel adapters with these connectors, unfortunately only one per unit (i.e. there is one unit available with the EMC XLR-3F and a conventional XLR-3M, plus another unit available with the EMC XLR-3M and a conventional XLR-3F; even Sescom's engineers couldn't explain why when I asked them). You might also try tightening any screws that could be any part of the connections among shields on your cables, microphones and recorder.
Ultimately, though, sorry to say, no one can guarantee a solution. Most audio equipment today, particularly in the consumer and "prosumer" ranges but including a lot of professional equipment, simply wasn't designed to handle the kind of interference that modern cell phones and related equipment can generate. Typical designs and production methods are often quite problematic (try doing a Google search on the "pin 1 problem"--even some top brands of studio equipment have had it, and much if not most "prosumer" equipment still does to this day). A new generation of design engineers, with a stronger awareness of electromagnetic interference, may will have to supplant today's generation of production designers before things get much better.
Or perhaps, since this problem doesn't affect most people most of the time, and most people don't shop specifically for equipment that's known to meet high standards of resistance to electomagnetic interference, the broad mass of equipment sold to the general market may never improve its resistance to EMI. Or the market may continue to muddle through as it has all these years, hoping that no one will blame them as from time to time we all, or nearly all, have recordings ruined in this way without there being anything much that we can do about it.