I have been dealing with this problem for over a year. I was initially told that xfinity had installed a new spam filter and senders of frequent emails were being considered spam. This included health systems, retailers, utilities, etc. I freelance for two health systems, so work requests were going to my spam folder. I use Outlook for email, which meant, at the time, I wasn't checking email on the xfinity site - until clients started calling and asking if I had received their emails. I also wasn't receiving bills. After many hours on the phone with xfinity, I was told to create filter rules so the emails would go to my inbox. This worked for a while, but in the last month, it's started happening again, even for email addresses I created filter rules for. It's infuriating and I refuse to sit on hold only to talk to someone who tells me to do the same thing I already was doing. So, I've turned off spam filtering and I check email on the xfinity site, as well as Outlook, multiple times a day. Now I get every piece of spam email sent my way, which is also not ideal. I'd like xfinity to just fix their spam filter so I can have it turned on, but still get all my valid emails. It's pretty obvious to me what's spam and what's not, so I'm not sure why this is so difficult. I am beyond frustrated and annoyed with this situation.
Comcast should offer a way to whitelist senders, but they don't. They don't offer any way for users to adjust their spam filtering either. Filters only operate on mail delivered to the Inbox, so you can't use them to move mail from Spam to the Inbox.
Recently announced "whitelist" function: https://forums.xfinity.com/t5/Email-Web-Browsing/Address-Book-Exemption/m-p/3368877#M220644
Is Outlook set up to use POP? If so, you could change over to IMAP instead (I'm assuming you mean the email program, and not the Outlook.com website). See https://www.xfinity.com/support/articles/pop-imap-microsoft-outlook and https://www.xfinity.com/support/articles/email-client-programs-with-xfinity-email. With IMAP, Comcast's Spam folder would be visible in Outlook.
You can move an email put into spam to inbox by clicking on "not spam" icon. That does not mean that Comcast will not dump that address into spam again. I can get multiple emails from the same person in a day, I Comcast will dump a couple of them into spam. I forwarded an email to myself, so same comcast email address, and it was dumped into spam. It ignores my address book. Many other email accounts into spam if email address is in address book. I do, though, have to compliment Comcast on their heavy spam filter. I seldom get actual spam