Biphasic p wave

Biphasic p waves can be a normal finding, particularly in V1 and III, or they can also be due to left atrial enlargement, so it's largely a non-specific finding. Whether or not a wave is upright or inverted depends on the direction the heart's electrical impulse is moving in relation to the point of view of the lead. As the electrical impulse travels, even if it's travelling in a basically straight line, it might be coming towards a lead's "eye" and then be going away from the "eye", sort of like if you're standing by the side of the road and a car comes by, it's coming towards then going away from you as it goes by.

If I find in lead two... Should I call doctor? Or it is not that significant?

No, I wouldn't call the doctor. It's something an EP doc might find mildly interesting, but no other Doc would typically care since it's typically chronic and not a sign of an acute change. It could go along with fluid overload, although we typically go by other indicators that are more relevant (lung sounds, edema, BP, CXR, etc)

A new finding of peaked P waves, an indicator of right atrial enlargement, in combination with respiratory compromise, could warrant notification since that could suggest a PE (the emboli backs up pressure into the RV and RA, causing dilation).