Lean on a stable surface to stabilize your shot whenever possible. Even if your phone already has optical image stabilization, this allows it to use an even longer shutter speed and/or lower ISO settings without your hand’s shakiness interfering.
Not taken with a phone but there’s no reason you wouldn’t be able to. Image Credit: Benson Chan /Flickr
If you really want to be serious, carry a small phone tripod for phones in your bag. If you’re shooting in manual mode, you can even set the shutter speed long enough for cool light trails.