An　ultra-sensitive　phase　plasmonic　sensor　combined　with　weak　value　amplification　is　proposed　for　the　detection　of　IgG,　as　a　model　analyte.　Phase　detection　is　accomplished　by　self-interference　between　the　p-polarization　and　the　s-polarization　of　the　light.　With　the　principles　of　weak　value　amplification,　a　phase　compensator　is　used　to　modulate　the　coupling　strength　and　enhance　the　refractive　index　sensitivity　of　the　system.　On　a　simple　Au-coated　prism-coupled　surface　plasmon　resonance　(SPR)　structure,　the　scheme,　called　WMSPR,　achieves　a　refractive　index　sensitivity　of　4.737　x　104　nm/RIU,　which　is　about　three　times　higher　than　that　of　the　conventional　phase-based　approach.　The　proposed　WMSPR　biosensor　gives　great　characteristics　with　a　high　resolution　of　6.333　x　10-8　RIU　and　a　low　limit　of　detection　(LOD)　of　5.3　ng/mL.　The　results　yield　a　great　scope　to　promote　the　optimization　of　other　SPR　biosensors　for　high　sensitivity.