Is biology an application of the laws of physics ? If you believe the laws of physics ultimately explain all physical phenomena then yes, it must be.
Are there grounds for this belief ? Well, so far we have not found any physical phenomena that definitely require something other than the laws of physics to explain them i.e. there is no empirical evidence for supernatural causes, for miracles, or for magic. And we know that biological phenomena follow regular patterns and can be investigated using the scientific method. Medicines do not come with warnings such as “will only work if you say the magic words and the stars are aligned properly”.
Do we know how some biological phenomena can be explained in terms of the laws of physics ? Yes, there is a whole field of study called biophysics that covers exactly this.
Do we know exactly and in detail how everything in biology can be shown to be an application of the laws of physics. No, not yet.
Is it a problem that we don’t know how exactly everything in biology is an application of physics ? No, not at all. Trying to reduce problems in biology to problems in physics is in many cases not a useful approach, even though we think it could be done in principle. By analogy, we know everything in cookery is an application of physics (since there is no magic pixie dust involved) but approaching every recipe as a physics problem will not get us very far.