as you are using a quad-pol product, i recommend to use the “select band” operator at the beginning and perform the workflow on HH first to test if everything works alright. The images you currently show include all polarizations, which does not make much sense at the beginning. Please check how phase quality can differ for the polarimetric bands: Effect of polarization on interferometric products
The SNAP workflow for polarimetry you described is working with single polarization images, so I recommend to repeat it with only one polarization at a time. Then your interferograms should look more typical (currently, you are displaying an RGB image of several bands).
Maybe also this tutorial helps you: Interferometry Tutorial with Radarsat-2 It was based on Radarsat-2 images, but the steps are the same for ALOS-2.