An organocatalytic controlled/living ring-opening polymerization (ROP) of 1,3,5-triphenyl-1,3,5-tri(p-tolyl)cyclotrisiloxane (PT3) using water or silanols as an initiator, 1,3-trimethylene-2-n-propylguanidine (TMnPG) as a catalyst, and organochlorosilanes or organoaminosilanes as end-capping agents was developed for the precise synthesis of symmetrically and asymmetrically terminated linear poly[phenyl(p-tolyl)siloxane] (PPTS) with controlled number-average molar mass (M_n), narrow molar-mass dispersity (Đ_M), and targeted terminal structures. The synthesis of PT3 was achieved by the reaction of dichloro(phenyl)-p-tolylsilane (PhpTolSiCl₂) and sodium hydrogen carbonate in dry toluene using simple synthetic procedures. The keys to controlling these ROP reactions are the use of THF as a solvent and the termination of the polymerization at the appropriate time. The precise synthesis of triblock copolymers of PPTS and poly(dimethylsiloxane) (PDMS), i.e., PPTS-b-PDMS-b-PPTS, was achieved by both the polymerization of PT3 using linear symmetric PDMS with two terminal silanol groups (PDMS-(OH)₂) as a macroinitiator and the two-stage polymerization of hexamethylcyclotrisiloxane (D3) and PT3. The synthesized PPTS and PPTS-b-PDMS-b-PPTS showed good solubility in various organic solvents. A thermal analysis of the synthesized PPTS revealed high heat resistance and fusibility.