Existing music and Apple Music

I have existing music on my iPhone that I dropped in from old CD's. I recently signed up for Apple Music, and there are some songs from Apple Music I'd like to add to my playlist. When I select the + option it tells me that it requires iCloud Music Library and it asks if I would like to Turn On. When I select Turn On it takes me to Enable iCloud Music Library, and it gives me the option to Keep Music or Delete & Replace. My only concern, or question is, are there any risks to merging with the iCloud Library? The songs I have on my phone are pretty old, and are not available on Apple Music (and since my old MacBook was stolen in Paris--but that is a different story), I no longer have these songs saved on a computer. I would hate to merge libraries and lose all of my older music. Any help is appreciated!