So they are saying that because the patient missed the 1 day they won't pay any of the other days? I don't have experience with this specifically, but I would make sure you are clear on the exact reason for the denial. If that were the denial why would they not pay all of the dates leading up to the missed day? Sometimes the denial is incorrect so that is why I'm asking.
If that is the denial, then I would appeal citing the reason the patient missed the 1 day. For example, if the patient had a stomach virus and was vomiting, etc. Or if the patient had a funeral to attend. If there is a valid reason for the patient missing then I would appeal based on that.
Another thing is you could ask for the patient's benefits. Meaning, does it state in their policy that PHP is only covered IF the patient has consecutive visits and is not covered if a date is missed.