To address the low phosphorus availability in acidic soils and the difficulty of precise pH regulation, this study used a typical acidified Eucalyptus plantation soil from Guangxi, China. Calcium oxide (L), rice straw biochar (C), organic fertilizer (O), and their binary combinations were selected as soil amendments. A laboratory incubation experiment was conducted under target pH levels of 5.5, 6.0, and 6.5. Soil pH, total phosphorus (TP), available phosphorus (AP), iron-bound phosphorus (Fe-P), aluminum-bound phosphorus (Al-P), exchangeable acidity and its components, exchangeable base cations, soil organic matter (SOM), and cation exchange capacity (CEC) were measured. The effects of different amendments on phosphorus availability and physicochemical properties of the acidic Eucalyptus plantation soil were compared under the same target pH conditions, and Pearson correlation analysis was conducted to examine the relationships among the measured soil properties. The results showed that the actual soil pH values after incubation were generally close to the target pH levels. Under the same target pH conditions, treatments containing organic fertilizer produced the largest increases in the soil phosphorus pool and AP content At pH 6.5, the contents of TP, AP, Fe-P, and Al-P contents in the O treatment were 9.1, 56.9, 189.5, and 7.9 times those of CK, respectively, while the AP contents of the L+O and C+O treatments reached 197.5 and 213.5 mg/kg, respectively. Among the treatments without organic fertilizer, the C treatment significantly increased Fe-P content only at pH 6.0 and pH 6.5. The C and L+C treatments significantly decreased Al-P content, with the C treatment reducing Al-P by 51.9% compared with CK at pH 6.5. All amendment treatments significantly reduced exchangeable acidity and exchangeable aluminum, by 80.6%–97.3% and 87.4%–98.5%, respectively, and the reductions under the L and L+C treatments were relatively consistent across the three target pH levels. The C treatment produced the largest increases in SOM and CEC, which reached 377.2 g/kg and 71.4 cmol/kg at pH 6.5, respectively. The O treatment produced the largest increase in exchangeable K?, while the C, O, and C+O treatments produced relatively large increases in exchangeable Ca²?. Pearson correlation analysis showed that AP was significantly correlated with TP, Fe-P, Al-P, and some exchangeable base cations, while pH was significantly negatively correlated with exchangeable acidity and exchangeable aluminum. Overall, under the same target pH conditions, different amendments still exhibited material-specific effects. Exogenous phosphorus input, organic carbon supplementation, and the redistribution of base cations may be important non-pH factors affecting phosphorus availability in acidic soils. These findings provide a theoretical basis for the precision management of soil pH and fertility in acidic forest soils. However, Pearson correlation analysis cannot directly establish causal relationships, and the underlying mechanisms and field performance require further validation.