How does the pulse phase influence NMR/NQR excitation?

[CristianM]

Hello! I'm studying nuclear quadrupole resonance (similar to NMR) and I am trying to understand the notation of the excitation sequences used in NQR spectroscopy. For example, the SLSE sequence is generally expressed as

I know that teta is the flip angle and is directly proportional with the pulse duration, but as I understand, phi represents the pulse phase. If that is the case, then why does the pulse phase matter in an experiment? I am asking because I do not understand how it can influence the excitation.

Or is it related with the phase used in the quadrature receiver for the sine and cosine reference signals? I've seen this phase having both positive and negative values in some papers.

I've seen complex sequences that enable cancellation of coherent noise caused by magneto-acoustic, piezoelectric signals and coil ringing, that use pulses with various phases in a specific sequence. I am trying to understand the phase parameter in order to understand these complex sequences.