The study sought to investigate the internal cycling of phosphorus (P) in Clementine mandarin (Citrus reticulata Blanco “Clementine”). The biomass formation, P concentration, P uptake and accumulation of different organs (bud, flower, fruit, leaf and branches) identified as active organs and found on 1-year-old shoots on fruit trees of bearing age were periodically examined for 2 years. The biomass value was similar between both production seasons. At the beginning of shoot activity, the biomass of annual shoots had a very low rate in the total biomass (0.4%). The biomass increased from 9.7 kg/tree at the beginning of the production season to 62.8 kg/tree at harvest. The P concentrations were in the ranges of 0.11–0.22% in the branches of <1-year-old shoots throughout the 2 years, 0.07–0.15% in the branches of 1-year-old shoots, 0.17–0.31% in the leaves of <1-year-old shoots and 0.13–0.26% in the fruits of <1-year-old and 1-year-old shoots. The total P accumulation at harvest was 82 and 107 g/tree in the first and second years for <1-year-old shoots, respectively, while it was 44 and 48 g/tree for 1-year-old shoots, in the first and second years respectively. The mean daily P uptake amount was determined as 0.4 g/tree for both production years, and the highest daily P accumulation amount was between the fifteenth and twenty-eighth days for both production seasons.