<p>Exploring the transient dynamics of ultrafast pulses is a fascinating frontier in ultrafast science. However, measuring rapidly varying spectrotemporal and phase information remains challenging. Here, we present an extracavity spectral phase editing method for the continuous generation of on-demand pulses and the experimental reconstruction of the wavelength-resolved phase dynamics of ultrafast pulses in a fibre laser. We first tailor a coherent, chirp-free seed spectrum into one or more sets of spectral combs. By controlling their interference, we generate diverse extracavity soliton compounds, including soliton molecules (SMs) and soliton molecular complexes (SMCs). Subsequently, we experimentally execute the equivalent round-to-round phase accumulations on the SMs and SMCs to reconstruct the various transient 32-pm-resolved phase dynamics, including oscillating phase, oscillating separation, combined oscillating phase and separation, and sliding phase, respectively. The experimental results show good agreement with previously reported findings. Our study provides a technique for both generating on-demand pulses and reconstructing transient wavelength-resolved pulse phase dynamics.</p>