The Shulhan Aruch (Orah Haim 232:1) says that if time is pressing, the congregation should recite the silent Amida of Minha and then the Shaliah Tzibur should recite only the first three blessings during his repetition of the Amida. Nevertheless, the Bet Yosef (§ 234…not 232?) points out that this is not the custom, but rather the congregation recites the first three blessings together, then continue the Amida silently until “Retze” and “Modim”, which is again recited in unison. In this way, the silent Amida is fulfilled as is the obligation to pray with a Minyan. Although our Sages instituted that the Amida should be repeated by the Shaliah Tzibur, the Rambam (Shu”t Pe’er Hador, § 148), Rabbi Shlomo Duran (Shu”t HaRashbash, § 56) and the Rabbi Moshe di Trani (Shu”t HaMabit, § 190) all write that if everyone in the congregation is proficient in the prayer, the repetition could be skipped if necessary. Indeed, Rabbi David Ovadia (Nahagu Ha’am, Tefilat Shaharit UMinha, § 19), Rabbi Yitzhak Hazan (Yehave Da’at) and Rabbi Baruch Avraham Toledano (Sha’alu LeBaruch, § 42) write that the custom in Morocco was to be lenient with repeating the Amida if time did not permit.
It should be noted, however, that on a Kabbalistic level, there is great value to reciting the Amida silently and then for it to be repeated aloud by the Shaliah Tzibur. Another benefit of repeating the Amida, the Rishonim write, is that one is able to recite Modim DeRabanan, which is one of the main purposes of the repetition.
Interestingly, Rabbi David Cohen–Scali (Kiryat David Hana, vol. II, § 1) a difference between the Ashkenazic and Sephardic custom is when the congregation begins reciting the silent Amida when there is no repetition. In the Ashkenazic custom, the Shaliah Tzibur recites the first three blessings and the congregations responds, and then each person recites the silent Amida from the beginning. In the Sephardic custom, each congregant begins the silent Amida along with the Shaliah Tzibur’s recitation of the first three blessings. The question is raised as to how a Sephardic person should conduct oneself when praying in an Ashkenazic Minyan when the Amida is not repeated. Practically speaking, it would appear that one should not begin the silent amida along with Shaliah Tzibur, but rather begin the silent Amida after the Shaliah Tzibur’s recitation of the first three blessings, just as the other congregants in such a synagogue do.
Furthermore, in prayers which contain Birkat Kohanim, such as Shaharit or Mussaf, if the Amida is not to be recited, the Moroccan custom is for the Shaliah Tzibur to recite the abridged version (“Elokenu Veloke Avotenu Barechenu Baberacha…”) out loud.
Summary: Although there is great value to the Shaliah Tzibur repeating the Amida, if there are time constraints, the custom is to be lenient and forego the repetition. The Sephardic custom is for the the entire congregation to begin reciting the silent Amid along with the Shaliah Tzibur.