Within Phantom, it's important to note that in your primary balance view, you’ll see the total BTC balance you hold in your addresses (Including all the UTXOs of rare sats, ordinals, and BRC20s). However, the actual available amount for sending or spending will depend on the actual amount on your Bitcoin addresses that spendable in normal Bitcoin transactions. Phantom excludes what are known as protected sats which represent other assets like Ordinals NFTs, BRC20 tokens, and rare sats. Again, you can learn more about Phantom's sat protection here.
Another reason why you might be seeing a different balance is because your accounts in Phantom only have two Bitcoin addresses (Native Segwit and Taproot), this means that if you’ve restored your wallet using a Secret Recovery Phrase from a traditional Bitcoin wallet (e.g. Electrum) you won’t be seeing the same global balance you have in those traditional wallets because on some wallets, your funds could be spread out between several addresses that you won’t see in your Phantom wallet’s accounts. In the traditional wallets you have several Bitcoin addresses (and change addresses), while on Phantom you only have one of each type per account. You’ll need to use a traditional Bitcoin wallet to consolidate[1]⚠️ all your BTC funds to one of the first addresses if you want to be able to use Phantom to interact with Bitcoin dApps using your “Payment address” (Native Segwit) and “Ordinals address” (Taproot).
[1]⚠️ Before using a traditional Bitcoin wallet to consolidate your Bitcoin funds by moving all of them to one of the first addresses, make sure you are using a Bitcoin wallet that recognizes Ordinals, BRC20 tokens, and rate sats correctly or you could destroy them in the process.