The Shulhan Aruch (Orah Haim 124:10) writes that if one forgot to include Ya’aleh Ve’yabo in the Amida on a day when its recitation is required, such that his Amida is invalid, he should fulfill his obligation by listening to the Hazan’s repetition of the Amida. He should stand next to the Hazan and carefully listen to each word, having in mind to fulfill his requirement by listening. He does not respond “Baruch Hu U’baruch Shemo” as he normally would, as this would constitute a Hefsek (interruption). After the Hazan completes the repetition, the person recites “Oseh Shalom.”
Most later Poskim, however, do not recommend fulfilling one’s requirement nowadays in this fashion, because it is exceedingly difficult to concentrate on every word of the lengthy Amida, as this would require. Therefore, a person whose Amida recitation was disqualified due to the omission of “Ya’aleh Ve’yabo” should recite the Amida a second time, rather than rely on his hearing the Hazan’s repetition.
Hacham David Yosef, in Halacha Berura (vol. 6, p. 290), notes that there are a number of situations in which one should fulfill his obligation by listening to the Hazan’s repetition of the Amida. One such situation is where someone recited the Amida properly but failed to concentrate on the meaning of the words during the first Beracha of the Amida. The Shulhan Aruch rules that an Amida recitation is invalid if the first Beracha was recited without Kavana (concentration), and thus the person in such a case must repeat the Amida. Common practice, however, is not to repeat the Amida in such a case, as it is likely that one who did not have Kavana during the Amida will not have Kavana the second time, either. Hacham David writes that the person in this case should listen carefully to the Hazan’s repetition and thereby fulfill his obligation.
Another situation is where one is uncertain whether he recited “Barech Alenu” in the Amida during the winter months, when this text is required. After thirty days have passed since Shemini Aseret, Halacha allows one in such a situation to assume that he has already grown accustomed to reciting “Barech Alenu,” and so this is the text that he recited. However, Hacham David writes, if the person is uncertain, then it is recommended that he carefully listen to the Hazan’s repetition of the Amida in order to fulfill his obligation in case he had not recited the Amida properly.
When fulfilling one’s requirement in this fashion, by listening to the Hazan’s repetition, he does not recite “Modim De’rabbanan,” and instead listens to the Hazan’s recitation of Modim.
Summary: As a general rule, one should not fulfill his obligation to recite the Amida by listening to the Hazan’s repetition of the Amida. If, however, one recited the Amida without concentrating during the first paragraph, then he should fulfill the obligation by standing next to the Hazan during the repetition and carefully listening to each word. Another exception is when one is unsure whether he had recited “Barech Alenu” instead of “Barechenu,” thirty days or more after Shemini Aseret. In this instance, too, one should listen closely to the Hazan’s repetition to fulfill the obligation, in case he had not recited the Amida properly.