As Phantom wallet, I never used it, appears to be BIP39 compatible, it should be no big deal to brute-force the missing word in between your known sequence of 11 words.

The last word of mnemonic recovery words according to BIP39 standard, embeds a checksum. When you say, some word in between is missing and the missing word position is unknown, there should be a rather limited amount of possible solutions.

I haven't done this for other coins than Bitcoin, but I assume it should be possible to brute-force the missing word with BTCrecover which can also handle Solana. If you know an address of your wallet, the better!

See here: https://btcrecover.readthedocs.io/en/latest/

You may need to make yourself familiar with the tool. If you know nothing about derivation path and HD wallets, then maybe learn about it at https://learnmeabitcoin.com. You can learn such wallet basics with no issue in the context of Bitcoin, even when your wallet was one with Solana.