Phen is a district in the northern part of Udon Thani province, Isan, Thailand. Neighboring districts are Sang Khom, Ban Dung, Phibun R…Phen is a district in the northern part of Udon Thani province, Isan, Thailand. Neighboring districts are Sang Khom, Ban Dung, Phibun Rak, Mueang Udon Thani, Ban Phue of Udon Thani Province, Sakhrai, Mueang Nong Khai and Phon Phisai of Nong Khai province.