No, loading phases aren't necessary, but they are used for quick saturation.
Loading phases consist of supplementing with 20-25 grams of creatine per day for five to seven days.
Once the loading phase is complete, continue with a maintenance dose of 3-5 grams per day.
If you don't want to use a loading phase - supplement with 3-5 grams per day, even on rest days.
Related Content:
Blog: Effective Creatine Loading - A Guide For Beginners
Blog: How Much Creatine Should I Take?
Blog: The Ultimate Guide to Everything Creatine
Blog: Debunking the Top 10 Creatine Myths