If your phone has a microSD slot (which is quick becoming a rarity), you might want to check out the SanDisk 400GB microSD card. It started at a hefty $230, but you can now have it for $190.
There are smaller cards too, the 256GB ones start at $100 if you don’t need so much storage (there are faster, pricier versions of the 256GB card too).
The 64GB and 128GB cards get you the most bang for your buck, we did the math:
The best deal on SD cards I've ever got was $19 for 128 SanDisk at OfficeDepot.
Meh, I got a 512G one :) https://www.mymemory.co.uk/memory/memory-cards/micro-sdxc.html?capacity=215
buy from a reputable supplier (who will replace without question!), so you don't get counterfeit..