I mentioned I am using the Blockchain app for iPhone.
My understanding of the bitcoin core app is that I need to be running a full node which is not advisable on my macbook air.
My understanding of RBF is that it needed to be enabled from the wallet that I originally sent the transaction from (so too late for that I think).
My understanding of accelerators is that they are hit and miss (and expensive with no guarantee).
It's already been over 3 days stuck but I didn't realize I was re-broadcasting it every time I opened the wallet. I suppose now I can try waiting a number of days without opening any of my wallets, and checking the progress on the blockchain website only.
For the blockchain app, it doesn't matter how often you open it, as the transaction is broadcasted by the backend servers of blockchain.info anyway. Your iPhone is only a client to their webservice, which operates independently. You can open it, it's the same effect.
Yes RBF has to be supported and enabled. Don't know if blockchain has it enabled.