Which phase of adolescence is characterized by rapid biological changes, high levels of stress, and relatively low coping abilities?

Early adolescence.

Explanation:

Early adolescence may be defined as the stage of 11 to 12 or 14 years of age. The physical change of the body is started at this stage. The secondary sexual characteristics and reproductive development commences in this stage.

The hormones has much influence on the body at early adolescence. The fast biological changes, low coping abilities and high level of stress is maintained at this age.

Thus, the answer is early adolescence.