Phantom has implemented a new feature that allows auto-speed up of transactions should the network gas fee environment change soon after signing. What this means is you do not have to manually come back to your transaction to rebroadcast it with higher gas limits (which is standard on most wallets today).
If you do not enable this option on a transaction, you can still manually speed up a pending transaction by going to the activity tab ⚡on the bottom-right corner of Phantom, then open the pending transaction, and tap Speed Up. This is for Ethereum and Polygon networks (EVM) only.