I found several interesting posts from Jeremy Crawford:
Object moving with target: Jeremy Crawford approved that the created object moves with the target.
http://www.sageadvice.eu/2015/09/14/phantasmal-force-on-a-bag/
Fighting creature moving: Analogous to that I would rule that if you create an hostile creature that is attacking the target, this creature would not be bound within the 10 foot are of the spell. It would follow the target, if that is trying to escape, because the creature is within the target's mind. Consider that the "conjured" creature must be not larger than 10 foot, but not the area that it is able to move, etc.
Creating Phenomena: Also it seems possible to create phenomena with Phatasmal Force. So, you could argue that an burning object consists of two things: object + fire. That's what the DM has to decice. For me as a DM, it would be okay, if you want to create a glowing cage.
http://www.sageadvice.eu/2015/09/14/blinding-phantasmal-force/
Object moving with target: Jeremy Crawford approved that the created object moves with the target.
http://www.sageadvice.eu/2015/09/14/phantasmal-force-on-a-bag/
Fighting creature moving: Analogous to that I would rule that if you create an hostile creature that is attacking the target, this creature would not be bound within the 10 foot are of the spell. It would follow the target, if that is trying to escape, because the creature is within the target's mind. Consider that the "conjured" creature must be not larger than 10 foot, but not the area that it is able to move, etc.
Creating Phenomena: Also it seems possible to create phenomena with Phatasmal Force. So, you could argue that an burning object consists of two things: object + fire. That's what the DM has to decice. For me as a DM, it would be okay, if you want to create a glowing cage.
http://www.sageadvice.eu/2015/09/14/blinding-phantasmal-force/