Poly(ethylene glycol) (PEG) polymers and PEG-conjugated lipids are widely used in bioengineering and drug transport applications. A PEG layer in a drug carrier increases hydrophilic repulsion, inhibits membrane fusion and serum opsonin interactions, and prolongs the storage and circulation time. It can also change the carrier shape and have an influence on many properties related to content release of the carrier. In this paper, we focus on the physicochemical effects of PEGylation in the lipid bilayer. We introduce laurdanC as a fluorophore for the shape recognition and phase transition detection. Together with laurdanC, cryo-TEM, DSC, molecular dynamics (MD) simulations, and SAXS/WAXS, we acquire information of the particle/bilayer morphology and phase behavior in systems containing DPPC:DSPE-PEG(2000) with different fractions. We find that the PEGylation leads to two important and potentially usable features of the system: 1) spherical vesicles present a window of elevated chain melting temperatures and 2) lipid packing shape controlled liposome-to-bicelle transition. The first finding is significant for targets requiring multiple release sequences and the second enables tuning the release by composition and PEG polymer length. Besides drug delivery systems, the findings can be used in other smart soft materials with trigger-polymers as well.