Your team needs to know how these phases match up for a web application project. The phases are somewhat similar, but without the sometimes lengthy timeframes previously seen in the industry. And if you want to limit risk, you need sound planning and management like in any other software project. Even speed is similar in the sense that marketing always wanted the product yesterday. The best way to reduce the risks when testing a web application is to add formal test planning and analysis to the beginning of the project life cycle.
Every project has testing at the end of the project life cycle.
Adding test planning to the beginning of the project life cycle will allow testers to prioritize their testing efforts based on risk, schedule constraints, and testers' abilities and aptitudes. This will be crucial to managing the test effort when the time crunch hits prior to going live. Now Testing a web page with relatively static content and few to no forms will take very little time. Testing a web application will require much more sophisticated testing strategies and thus more time. Due to the nature of web development, your team probably won't get more time and maybe even less than for a traditional development project.