ASP and PHP are web programming language which is viewable by web browser. But host or server is different history. PHP runs on linux which is called LAMP and ASP runs on windows by IIS(Internet Information System) service.
Mostly use MySQL database
Best use for small development
Tons of open source CMS
Software are free, only pay for hardware.
Can create nice graphics and easy to build websites and portal.
Use MSSQL database
Best uses for large development
Some free CMS, mostly paid
Need to pay for windows server, MYSQL, Visual studio and hardware.
Mostly programming and complex development.
We also decide development process by organization size, user preference and budget. You might get more difference if you research at online. But you can have PHP with large database if you use paid system other-side most complexity might easily solved by ASP language.