Murphy, John,Pvt. 2nd Lt. Field and Staff, 8th La. Inf. En. June 19, 1861, Camp Moore, La. Present on Roll to Aug., 1861. Apptd. Corpl., Aug. 21, 1861. Roll Nov. and Dec., 1861, Present. Roll Jan. and Feb., 1862, Absent, detached as Q. M. Sergt. Rolls June, 1862, to Aug., 1862, Present. Elected Lt. May 4 from 3rd Sergt. Rolls to Feb., 1863, Absent, wounded at Battle of Sharpsburg. Rolls to May, 1863, Present. Rolls to Dec., 1863, Absent, wounded at Battle of Gettysburg. Record copied from Memorial Hall, New Orleans, La., by the War Dept., Washington, D. C., June, 1903, born Ireland, occupation mechanic, Res. Port Hudson, La., age when enlisted 23. Killed Battle of Wilderness, May 5, 1864.
From reading Booth's information, it appears he was a Private, then on Staff as a 2nd Lt. I could be wrong, and more knowledgeable people might know better if I am reading this right. It looks like he went down to a Corporal, the detached as a QM Sgt. Futher along he was a 3rd Sgt, then a Lt. Normally company officers were elected, so he may have been in a Company, but Booth's does not say which one. Looking at Bergeron's book on Louisiana units there is no company officer noted with that last name. But the listing only references Company Commanders, not subordinate officers.
Looking at muster rolls put together by Wayne Cosby, there is a John Murphy in Co A. My guess is that perhaps he was in Co A initially. This as the 'other' Murphy's are also identified by their middle initial.
My guess is you might have to order his records (see above), that might answer your questions.
JIM T