It is the opposite in fact. I have had 4 wireless rechargeable devices and they get a lot hotter than wired charging as well as been slower. You can overcome the slowness part by basically beginning with a lot more energy, which is why wireless chargers do make sense but it makes no sense for a wireless portable charger. You'd be better off carrying a small wired charger like the cheap single-recharge Mini, or two-charge Powercore II 6700, if you want it flat the Slim 5000. Anker doesn't particularly offer very short cables so I have non-Anker cables for the recharging phone while in use situations.
What is causing the heat is the unwanted induction in the metal in the phone plus proximity conductance of the heat off the charger touching and transmitting heat into the phone. Some Anker wireless chargers mitigate that via making a stand so hear can convect away.
This inefficiency would get better if they made phones with less metal and if the frequency of the wireless charging were to increase. The problem then is you're making radiation in frequencies where it risks interfering with radio signals, emergency services, cellular, etc.
Wireless charging is about 90% efficient so there's your problem if you had a trickle charge say 5W you're creating about 0.5W of heat, but if you make a fast charger like 20W then its 4W of heat in a relatively confined volume of a phone which the cpu 2-6W and bursts up briefly and shuts down cores to give time for heat to conduct away, while charging you're going to have watts of heat for minutes to hour.
I suspect what would work better is robotic parabolic transmitters which follow you round a room and send a focused pulse to your phone, or ultraviolet lasers but then you're adding risk of cancer.
Stick with wires I say.
Let's put it this way, your human body evolved with wires (the nervous system) and evolution didn't decide the brain would transmit muscle signals from the skull to your toes wirelessly due to the energy loss. Now consider the evolutionary risk of wires, you sever a nerve at any point the length of your body you're paralyzed to the end of the wire so there are very good efficiency gains from wires.