According to the notice of the death of Jack Phillips
both he and his father Leonard had served in the same company of the Territorials as his father and had rejoined at the outset of the war.
The 1st Battalion of the Birmingham Rifles becamme the 5th Battalion, Royal Warwickshire Regiment in 1908, Jack's Battalion. Therefore it seems that Jack and Leonard belonged to 1st Battalion of the Birmingham Rifles.
Jack must have joined before 1910 (when he was 20 or less) and he served 4 years.
On the face of it Leonard joined before 1876 and served for 34 years, retiring before Jack joined. However, this would make him 14 or less when he joined. That seems unlikely and therefore it is more likely his 34 years ended about 1914 and he joined about 1880, when he was 18.

Following an invasion scare in 1859 many Rifle Volunteer Corps (RVCs) were formed composed of part-time soldiers. One such was the 1st (Birmingham Rifles) Warwickshire RVC formed on 20 October 1859. Two other RVCs were absorbed the following year and the unit soon reached 12 companies. Some recruited from particular trades. There was for a time a Cadet Corps at King Edward's School.
At first the uniform was grey with green facings, then Rifle green with red facings. The headquarters and drill hall was at Thorpe Street.

Under the 'Localisation of Forces' scheme introduced by the Cardwell reforms (1868-1874), the Volunteers in Warwickshire were grouped with the two Regular battalions of the 6th Foot (Royal Warwickshire Regiment) and the two Warwickshire Militia regiments into Sub-District No 28 (County of Warwick), forming Brigade No 28 (Warwickshire).

Following the Childers Reforms, the battalion was designated the 1st Volunteer Battalion of the Royal Warwickshire Regiment in 1883. Four new companies were added in 1891, the unit reorganising as a double battalion, the 1st Battalion having 'A' to 'H' Companies, the 2nd 'I' to 'Q' Companies.

A cyclist section formed in 1894 had become a full company by 1900, together with 'U' Company formed of staff and students of Birmingham University. New cadet corps were formed at Solihull Grammar School and King Edward's School in 1904 and 1907 respectively.

The Stanhope Memorandum of 1888 proposed a Mobilisation Scheme for units of the Volunteer Force, which would assemble by brigades at key points in case of war. In peacetime the brigades provided a structure for collective training.

The Volunteer Battalions of the Royal Warwickshire, Leicestershire, Worcestershire and Northamptonshire regiments were formed into a South Midland Volunteer Infantry Brigade, which in the event of war was to assemble at Warwick. Later a separate Worcester and Warwickshire Volunteer Infantry Brigade was formed.

The Volunteer battalions of the Royal Warwickshires provided volunteer service companies to serve alongside the Regulars during the Second Boer War, earning the battalion its first Battle Honour: South Africa 1900–02.

When the Volunteers were subsumed into the Territorial Force (TF) in 1908 as part of the Haldane Reforms, the 1st and 2nd Battalions of the Birmingham Rifles became the 5th Battalion, Royal Warwickshire Regiment and 6th Battalion, Royal Warwickshire Regiment respectively, while 'U' Company and the cadet corps became part of the Officer Training Corps. The battalion adopted the red uniform with blue facings of the Royal Warwickshire Regiment. Both the 5th and 6th battalions were in the Warwickshire Brigade of the TF's South Midland Division.