Microservice is an architectural style that breaks down monolithic applications into smaller microservices and has been widely adopted by a variety of enterprises. Like the monolith, autoscaling has attracted the attention of operators in scaling microservices. However, most existing approaches of autoscaling do not consider microservice chain and severely degrade the performance of microservices when traffic surges. In this paper, we present pHPA, an autoscaling framework for the microservice chain. pHPA proactively allocates resources to the microservice chains and effectively handles traffic surges. Our evaluation using various open-source benchmarks shows that pHPA reduces 99%-tile latency and resource usage by up to 70% and 58% respectively compared to the most widely used autoscaler when traffic surges.