1. Adding an SD card won't really give you more storage. (It definitely won't give you more memory - RAM - because it has nothing to do with memory, it's storage. And they're
not the same thing.)
2. SanDisk is the inventor of the technology, and one of only 2 companies that produce the chips in the card. And they have what I can only call fantastic customer service. (I never worked for them - I pay retail or Amazon price for all my cards.) If you ever have a problem with their car (the only problem I ever had, in years of using their cards, was a card I snapped in half - that's not covered by the warranty.) Go to
SanDisk microSD Tech Support and look in the upper right corner for Chat Lice. You'll be talking to a real tech. And if s/he determines that the card
is defective, they'll give you instructions (and take your name, address, etc.) for a replacement.
3. The phone being refurbished doesn't make any difference. (My current phone is the 3rd refurbished phone I've gone through - and the SD card still works perfectly.)
4. If you want the best card for that phone, and it's 64GB or larger, get an SDXC U1. (You only need a U3 if the phone can do 4k video, which that one can't.) If it's smaller than 64GB it's going to be SDHC. (The designations are related to how large the card is [electrically].)
5. Plan on putting data - documents, pictures, music and videos - on the card. That gets them off the phone itself, and gives you a little more space for apps. (Apps "moved" to the card don't, actually. Small pieces are moved, but they leave "links" to the moved pieces in the phone, so unless the pieces are large compared to a link [and most aren't], you aren't gaining much space. Moving a file to the card just moves the entire file. [Don't use move", though - use "copy". If the copy is successful, delete the original (in the phone). If a copy blows up, you still have the original, if a move blows up you can lose both the original and the copy.])
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