Yes, on at least three occasions.
Know what happens when a character who is most known for only saying "I am Groot" gets Venomized? Well, Guardians of the Galaxy #21 (2014) has your answer.
He says "I am Venom".
Another time was in Venom: Along came a Spider #1 (1996). Eddie Brock disguises himself as detective Clark from the NYPD (using the Symbiote), and drops the mask, revealing himself as "I'm Venom".
Clark/Eddie: Don't pull down on the little twerp - he's not Venom!
Steen: How do you know, Clark?
Eddie: Because I'm Venom!
As far as I know, the first time the "I'm Venom" phrasing was used was in 1993, in Venom: The Madness #2. After agreeing to bond with the "living mercury" contained in a pool Juggernaut had thrown him in (what? It doesn't sound like a reasonable idea to you?), Venom got some kind of an upgrade and sought out an innocent to save, introducing itself as "I'm Venom".
Granted, in this case the "I'm Venom" wording instead of the usual "We are Venom" might be due to the demons playing with his mind through the living mercury.