Yes! There is a bunch of flip and more so, basic phones that can give you access to WhatsApp. Whatsapp is designed to not only offer internet access to smartphones but also flip phones.
If you have access to a recently manufactured flip phone, you may notice the cool interface and support for modern apps. This is because most phone manufacturers are trying to bring a digital experience to basic phones.
Verizon recently launched a flip phone with support of 4G LTE network technology. The phone is way better compared to the flip phones that can give you access since it uses LTE network technology compared to the other flip phones that use 3G networks.