The SR-71 leaked because it was designed to leak. The titanium fuselage panels, including the fuel tank segments, were loosely fitted, with gaps, to accommodate the thermal expansion of the metal once the plane reached its high operating temperature. Once hot, the gaps were filled and the plane and its tanks were tight. Had the plane been designed without the gaps, thermal expansion would have warped the plane. They could not use rubber bladders in the tanks like in conventional planes, as those could not withstand the heat. The JP-7 fuel with its high flash point temperature was specially developed for the plane. Leakage on the ground was not dangerous and deemed an acceptable trade-off. The plane would get sufficient fuel on the ground to take off and warm up, and then receive a full fuel load in the air. The fuel leakage itself was not even the issue, as it did not leak that much; the problem was air getting into the tanks, creating an explosive fume mix that would have been dangerous at higher temperatures. Once the tanks were tight, refuelling them completely would vent out any air. To prevent fume buildup later on as the fuel got consumed, the tanks were continuously refilled from nitrogen containers aboard the SR-71, ensuring they had an inert atmosphere inside.
Ti-6AL-4V is by far the most common variant of titanium in everyday items. Watches, knife handles, golf drivers, entire bicycle frames are made of Ti-6AL-4V. It sure costs more than aluminium, but not so much to make it prohibitive for the consumer market. Besides, the titanium in the iPhones is just a millimeter thick. My little pocket knife probably has enough Ti-6AL-4V for five iPhones.
Besides, I doubt the titanium has much of a role in any overheating issues. Measurements show the iPhone 15 Pro going towards 50°C at peaks. That may be hot for a phone, but not for metals like titanium. Also, while titanium has less thermal conductivity than aluminium, it is much better than plastic or leather - so if a thin rim of thin titanium causes overheating, then phones in cases should have been overheating for years.
