I may be wrong, but I don't think you can delete it in the sense of uninstalling it from the phone. Perhaps you long-pressed the Phone icon unintentionally, and selected Remove? Open the app tray, and see if the Phone icon is there. If so, long-press it and move it to the left edge of the screen, to get it to take up a position on a home page.
If none of the above helps, let us know.
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