There are several applications of virtual reality (VR) that can be developed using PHP. Some examples include:

1. Virtual tours: PHP can be used to create virtual tours of real estate properties, hotels, museums, etc. Users can explore these spaces virtually and get a realistic experience.

2. Gaming: PHP can be used to create VR games, where users can immerse themselves in a virtual world and interact with the environment and other users.

3. Training and simulations: PHP can be used to create virtual training environments and simulations for various industries such as aviation, healthcare, engineering, etc. Users can practice their skills and learn in a safe and controlled virtual environment.

4. Education: PHP can be used to create educational VR applications where students can learn complex concepts in a more engaging and immersive way. This can include virtual science labs, anatomy lessons, historical recreations, etc.

5. Virtual meetings and collaboration: PHP can be used to develop VR applications that allow users to have virtual meetings and collaborate in a virtual environment. This can be particularly useful for remote teams or for conducting virtual conferences and events.

6. Healthcare and therapy: PHP can be used to develop VR applications for medical and therapeutic purposes. This can include VR therapy sessions for mental health, VR simulations for surgical training, VR experiences for pain management, etc.

7. Marketing and advertising: PHP can be used to create immersive VR experiences for marketing and advertising campaigns. These experiences can help businesses showcase their products and services in a more engaging and memorable way.

These are just a few examples of how PHP can be used in virtual reality applications. The possibilities are endless, and with the advancements in VR technology, we can expect to see more innovative applications being developed using PHP.