Is It Possible to Cancel the Quest "Call of the Sea"?

[Raltar]

Call of the Sea is your main story quest. Every class gets this quest and you need to complete it to continue the story. The quest underneath it will be your current class quest.

[qaija]

So just continue to do the quests below the MSQ in order to progress as a Conjurer? And thank you for your help.

[MsQi]

So just continue to do the quests below the MSQ in order to progress as a Conjurer? And thank you for your help.

You can do MSQ quests on whatever combat class you want as long as it is high enough level. That class will gain the experience.

EDIT: sorry, yes the one below the MSQ is the class or job quest. It will advance the class or job you currently are.

[Vidu]

So just continue to do the quests below the MSQ in order to progress as a Conjurer? And thank you for your help.

Yes, the mainquest is tied to your character, not your job.
You can have multiple jobs - infact all the jobs in the game - and you can switch between them freely (at least for 98% of all quests). You can follow the mainquest which whatever job you want - the job your on when you turn the quest in will recive the exp from that quest.
In theory you can follow the mainquest as thaumaturg now for a while and then switch back to conjurer or pick up a completly new job. As long as the job your on is highlevel enough to complete the quest, the mainstory doesnt care if you started out as conjurer but see the end as warrior.

In addition to that: Even quests that you cant complete with your current job wont disappear - if you picked up a conjurer-class quest, its still in your questlog, ready to be completed whenever you switch back to your conjurer. FFXIV is based around the idea that you can level all of the available jobs on one character. Progress with one job, wont delete the progress with different job and you can switch freely between by switching out your mainhand-weapon (or, a little easier: creating armor-sets to switch between them).

Little sidenote: Your forum-avatar shows that your character is a lancer - is this by choice or maybe a mistake with the forum? I'm asking because at level 55 you should look into unlocking dragoon, the job that the class lancer advances to. Each base-class (lancer, thamaturg, conjurer...) has a job they progress to after level 30 - you need to complete a special quest for each of those job, get the appropriate soul-crystal and should never ever go back to the base class again but keep thet soul-crystal equipped so that your lancer will be a dragoon, your thaumaturg will be a blackmage and your conjurer will be a whitemage (and so one for the others).

[Rongway]

So just continue to do the quests below the MSQ in order to progress as a Conjurer? And thank you for your help.

The red and beige meteor banner is a clickable map link to your current or next main scenario quest. The MSQ is a long running story arc spanning from A Realm Reborn (2.0) through Endwalker (expansion coming later this year). You can change classes as often as you want without affecting your progress in this arc. However, your MSQ progress will require that your current class or job is at least a high enough level to turn in the current MSQ.

Class quests, job quests, and other important side quests like the mount unlock quest will appear as smaller clickable map links below the red and beige meteor banner as they become available. Each combat class has its own quest arc starting at Lv1 and continuing every 5 levels from 5 to 30. Jobs have quests beginning at 30.