In terms of a foreigner who is a beginner in Japanese, this kind of phrase is certainly impressive, and it is basically correct.
However, since "jou" in "tanjoubi" and "tou" in "omedetou" are both in long-vowel sound, and since you have already used "jô" to represent the long vowel of "jou", I would say that it is better that you also use "tô" on "tou" to keep the consistency.
Therefore, it should be,
formal: "o-tanjôbi omedetô gozaimasu." = お誕生日 おめでとう ございます。
casual: "o-tanjôbi omedetô." = お誕生日 おめでとう。
Take care, and good day. / Mach's gut, und schönen Tag. / 気をつけて。それじゃ、良い 一日を。