We report on the carrier-envelope phase (CEP) stabilization of a Yb-doped fiber amplifier system delivering 30 μJ pulses at 100 kHz repetition rate. A single-shot, every-shot measurement of the CEP stability based on a simple f-2f interferometer is performed, yielding a CEP standard deviation of 320 mrad rms over 1 s. Long-term stability is also assessed, with 380 mrad measured over 1 h. This level of performance is allowed by a hybrid architecture, including a passively CEP-stabilized front-end based on difference frequency generation and an active CEP stabilization loop for the fiber amplifier system, acting on a telecom-grade integrated LiNbO3 phase modulator. Together with recent demonstrations of temporal compression down to the few-cycle regime, the presented results demonstrate the relevance of the Yb-doped high repetition rate laser for attoscience.