It's not uncommon for "hospitalists" to provide care when you are inpatient. Like other hospital-based physicians, they may or may not have a contract with your insurance company. If not, the insurance may only allow a "reasonable and customary" amount, which in turn could be applied to your deductible (I suspect that's what the $300 represents). The physician will then balance bill you for the difference between the R&C amount and the total billed charges, in addition to the deductible you're already responsible for.

I would advise you to contact your insurance company - start by calling the customer service phone number. Some companies even have a "Live Chat" feature on their member website (I love this because you can print a transcript of the chat). Many companies have a policy that they will reprocess the claim to allow full billed charges if the patient is being balance-billed by a hospital-based provider. Of course you may still be on the hook for the amount if you haven't met your deductible yet.