31st Infantry was one of three infantry regiments (and the only Regular Army infantry regiment) assigned to the Philippine Infantry Division. The regiment resisted the Japanese invasion and offensive on Luzon from 8 December 1941 to 9 April 1942 and was one of the many American and Filipino units that were surrendered to the Japanese on the latter date.
You can order his deceased file. You'll find practical instructions at Message #2112 (go back to the Main Page, enter "2112" in the box in the upper right corner marked "Jump to #_____" then click on "Go"). The file should include his date and place of death and burial even though he was a prisoner of the Japanese at the time (not long ago I researched a man who died shortly after the Bataan Death March; his deceased file contained a short affidavit written on what appeared to be a small piece of scrap paper by an officer who had witnessed the man's death. The file should also reveal his service number, company and other information of interest).
Your Uncle would be entitled to the following decorations and awards (in the proper order of precedence):
Bronze Star with "V" Combat Distinguishing Device Purple Heart Prisoner of War Medal Presidential Unit Citation with Oak Leaf Cluster Good Conduct Medal American Defense Service Medal with "Foreign Service" Clasp Asiatic-Pacific Theater Medal with one bronze service star (representing participation in the Philippines Campaign) World War II Victory Medal Republic of the Philippines Presidential Unit Citation Philippines Defense Medal with one bronze service star
All but the last two may be obtained free of charge from the NPRC St. Louis (may involve a wait of up to two years). Their website is at < http://www.nara.gov/regional/stlouis.htmlhttp://www.nara.gov/regional/stlouis.html >. The last two were awarded by the Philippines Government and must be purchased. I have access to a limited number of Philippine Liberation Medals.