These three laws hold to a good approximation for macroscopic objects under everyday conditions. However, Newton's laws are inappropriate for use in ... or very strong gravitational fields. - Newton's laws of motion (Wikipedia)
Is this line true? If so, how does being in the presence of a strong gravitational field affect the three laws?
Yes, it is true. In the presence of a strong gravitational field the curvature of spacetime is large (this is the definition of a 'strong gravitational field', in GR). If curvature is large then the distance and time over which you can treat spacetime as approximately flat becomes very small. That means that the distance and time over which it makes sense to talk about an inertial frame becomes very small, which in turn means that Newton's laws are approximately true only on very small scales, with the scale getting smaller as the field strength or equivalently curvature rises.