Unlike linear arrays, phased array transducers do NOT fire subgroups of elements to produce each scan line.
Phased array transducers fire all the elements together to produce each scan line. To do this, phased array transducers employ "electronic beam steering".
Phased array transducers typically have a smaller footprint than linear array transducers and are the primary type of transducer used in echocardiography.
Please watch my video on phased array transducers for more detail.