No definitive consensus on this one but given risk of proximal greater saphenous vein superficial venous thrombosis (SVT) progressing to deep vein thrombosis and/or pulmonary embolus some advocate for anticoagulation of this subset of SVT. If anticoagulation is not initiated, a repeat ultrasound in 3 - 7 days should be considered.
Source
Fernandez, L. MD. "Superficial phlebitis" Up to Date. 5 Sept 2008.