I am working through the last years of John Phethean & Co Ltd from documents at the National Archives, which I am gradually adding to this site.

This is what happened to the company post 1924:

1924 Offices: 30, George Street, Manchester; Cawdor Street, Farnworth, near Bolton. Spinners and manufacturers of Alhambra, honeycomb, tapestry, Grecian fancy quilts and honeycomb, toilet covers, plain and raised sheets, cotton blankets and blanketings.
Spinners at New Mills, near Stockport.
Bleach Works: Birch Vale, near Stockport.
Mills: Farnworth, near Bolton.

1929 Joined 6 other manufacturers to form the Quilt Manufacturers company, which became part of Vantona Textiles. The Quilt Manufacturers company was incorporated to acquire and amalgamate 7 of the leading companies in quilts, bedspreads, covers, etc :

Jabez Johnson, Hodgkinson and Pearson Ltd incorporating George Mort and Co
Jonathan Dearden and Co, owners of James Lomas Ltd
T. Taylor Ltd
James Kippax and Son Ltd
John Phethean and Co Ltd
Henry Bond and Co Ltd
Eccles Quilts Ltd

1936 The name of Quilt Manufacturers Ltd was changed to Vantona Textiles. Considerable reorganization and unification of control was implemented but would take some years to have full effect.
1947 Listed Exhibitor – British Industries Fair. Spinners, Dyers, Bleachers, Manufacturers of Vantona Household Textiles, Bedcovers, Quilts, Counterpanes, Bedspreads and Down Quilts, Cotton Blankets, Blansheets, Sheets, Towels, Towelling, Ticks and Ticking. (Earls Court, Ground Floor, Stand No. 286)
1951 Occupied Milton Mill, Mule Street, Tonge, Bolton, Lancashire.
1957 After a battle, Messrs Julius and Basil Glass of Everwear Candlewick acquired a controlling interest in the company
1959 Acquired Balstone Cooke and Rayonese
1960s Occupied Moor Mill, Parrot Street, Great Lever, Bolton, Lancashire.
1961 Merger with Richard Haworth and Co
1975 Acquired by Spirella as a reverse take-over.
1978 the Spirella brand became part of the Vantona Group.
1978 After a battle with others Vantona acquired J. Compton, Sons and Webb (Holdings)
1983 Acquired Carrington Viyella becoming Vantona Viyella
1984 Acquired F. Miller (Textiles)
1985 Merger of Vantona Viyella with Nottingham Manufacturing Co.
1986 Acquired Coats Paton becoming Coats Viyella

(Information from Graces Guide to British Industrial History)