Okay guys, first this must be said ... cooler heads, please. Even minor bickering will take this off track enough to not help the OP with his/her problem.
I think the confusion lies in that normally contact and call information is stored in a protected database that users wouldn't have access to unless rooted. I would suspect
@KBU2 that you have some sort of backup utility that is touching your contacts and backing them up to an SD card. I looked on my phone (LG G6 running Oreo) using X-plore file manager and I do indeed have a similar path to /root/storage/[volume label] and what it appears to be is a simlink to my SD card, because when I expand the folder it is all the content on my card only.
@ElisavetKat, rooting your phone won't miraculously make these contacts appear or give you access to some secret hidden backups. What I am confused about is that you say the number you are trying to retrieve was a dialed number that was not answered so it wouldn't be part of your carrier's records, but it may be. Have you contacted them to ask for a list of calls that weren't completed? If the phone rang on the other end, then it certainly hit their network and they'd have a record of it.
Was this number ever setup as a contact? If not, then looking in contacts or rooting your phone is useless. Also, as
@Hadron points out, rooting your phone will remove all user data which defeats the purpose of rooting it if you are trying to recover data. If you could possibly let us know what model you phone is, what version of Android it's running and who your carrier is, maybe we can point you in a better direction.