Make your call. If you are 100% certain F3 held the bag tell everyone as you are making your call: " He held it!" or something like that.
If you are not certain, make your call as you would normally. If anyone asks you to get help, call time if necessary and conference with your partner(s) so only the umpires are a part of the conversation. I am not a fan of yelling across the field to get input on a play. If no one asks you about a pulled foot or a swipe tag, the call belongs to you and stands as it was judged.