A reversible and easy assembled fluorescent sensor based on calix[4]arene and phenolphthalein (C4P) was developed for selective zinc ion (Zn2+) sensing in aqueous samples. The probe C4P demonstrated high selective and sensitive detection towards Zn2+ over other competitive metal ions. Interaction of Zn2+ with a solution of C4P resulted in a considerable increment in emission intensity at 440 nm (λex = 365 nm) due to the suppression of photoinduced electron transfer (PET) process and the restriction of C=N isomerization. The binding constant (Ka) of C4P with Zn2+ was calculated to be 4.50 × 1011 M−2 and also the limit of detection of C4P for Zn2+ was as low as 0.108 μM (at 10−7 M level). Moreover, the fluorescence imaging in the human colon cancer cells suggested that C4P had great potential to be used to examine Zn2+ in vivo.