Phillipps enlisted in the Australian Imperial Force in April 1915 and was assigned to the 28th Battalion, an infantry unit raised the same month at Blackboy Camp, Western Australia.
He successfully applied for a commission and left for Egypt aboard HMAT Ascanius on 9 June as a second lieutenant.
After training in Egypt, he departed with his unit for Gallipoli aboard the transport Ivernia on 4 September.
He was promoted to lieutenant on 25 October.
The 28th Battalion, which had been sent to Gallipoli late in the campaign as reinforcements, was not heavily engaged on the peninsula, and suffered relatively few casualties before the withdrawal in December 1915.

In March 1916, Phillipps was deployed to France with the 28th Battalion for service on the Western Front.
He participated in a raid against the forts of Armentières on the night of 6/7 June, and saw action during the Battle of Pozières in July.
On 5 August, he was shot through the thigh, requiring evacuation to England for hospital treatment.
He was promoted to captain on 12 August.
Phillipps rejoined his unit in October but suffered another gunshot wound to the thigh the following month, near Gueudecourt.
He returned to England once more to recover, and remained in hospital until 2 March 1917.
Phillipps enlisted in the Australian Imperial Force in April 1915 and was assigned to the 28th Battalion, an infantry unit raised the same month at Blackboy Camp, Western Australia. He successfully applied for a commission and left for Egypt aboard HMAT Ascanius on 9 June as a second lieutenant. After training in Egypt, he departed with his unit for Gallipoli aboard the transport Ivernia on 4 September. He was promoted to lieutenant on 25 October. The 28th Battalion, which had been sent to Gallipoli late in the campaign as reinforcements, was not heavily engaged on the peninsula, and suffered relatively few casualties before the withdrawal in December 1915.
In March 1916, Phillipps was deployed to France with the 28th Battalion for service on the Western Front. He participated in a raid against the forts of Armentières on the night of 6/7 June, and saw action during the Battle of Pozières in July. On 5 August, he was shot through the thigh, requiring evacuation to England for hospital treatment. He was promoted to captain on 12 August. Phillipps rejoined his unit in October but suffered another gunshot wound to the thigh the following month, near Gueudecourt. He returned to England once more to recover, and remained in hospital until 2 March 1917.
Roy Phillipps