The PHASE_OUT field is sign extended to the next multiple of eight bits and
becomes m_axis_phase_tdata. For example, if PHASE_OUT is 20 bits,
m_axis_phase_tdata is 24 bits wide [23:0], occupied by a sign
extended PHASE_OUT.
The following figure shows this for an example width of 11 bits sign extended to 16 bits.
Figure 1. Output PHASE Channel TDATA Structure