Both Sibson and Pheasant featured against Rugby last season for Dynamo in the league and join Jepson's squad ahead of his first season in management as Valley prepare for a second season in the EVO-STIK NPL's First Division South.
Centre-back Sibson, 24, is a former Nottingham Forest youth academy prospect who also lists Quorn and Long Eaton among his former clubs.
Pheasant, 26, operates as a right-back or centre-back and has enjoyed previous spells with the likes of Ilkeston, Hucknall, Mickleover and Quorn.
* Rugby Town are looking forward to hosting League One Coventry City on Tuesday 19 July in a 7.30pm kick-off after a 10-year gap since the Sky Blues last Butlin Road appearance. Visit the fixture pages for details of nearly 300 friendlies involving the EVO-STIK NPL's 68 clubs over the next five weeks.
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