Phillip Arthur Williams was a local coal miner and the second son of Mrs. Mary Jane Williams of Syr Dafydd Avenue, Oakdale, and the late Phillip Williams. He stepped forward to serve with the Territorial Force, enlisting into the 1st (Rifle) Battalion, Monmouthshire Regiment. He deployed overseas with his comrades, arriving on the battlefields of France and Flanders in February 1915.

In early May 1915, during the brutal opening phases of the Second Battle of Ypres, his battalion operated as part of the 84th Brigade, 28th Division, positioned directly to the right flank of the 12th Brigade. On 8 May, the brigade was dug into highly exposed forward slopes on the ridge running between Frezenberg village and the fortified ruins of Shell Trap Farm. Sitting right on the shoulder of the vulnerable British salient, they were subjected to a monstrous, concentrated artillery bombardment before being hit by waves of German infantry.

Vastly outnumbered and cut off from reinforcements, the units were slowly surrounded, fighting tenaciously before the remnants could fall back over the low crest of the ridge. The 1st Mons were virtually annihilated; out of 588 soldiers who stood in the lines that morning, 439 were killed, wounded, or reported missing. Private Williams was killed in action during this desperate defense on 8 May 1915, aged just 19.

Because his remains were swallowed by the shattered landscape of the salient, he is permanently commemorated on the panels of the Ypres (Menin Gate) Memorial, Belgium. He is also honored on the Battalion War Memorial inside St. Woolos Cathedral, Newport. Today, a dedicated memorial stands at Roeselarestraat, north-east of Ypres, honoring the 203 men of the battalion who perished on 8 May—a day remembered back home in the valleys as "Monmouthshire's Black Day."